KR20130028800A - Apparatus for producing alloying galvanized sheet steel and method for producing alloying galvanized sheet steel - Google Patents

Abstract

The alloying hot dip galvanized steel sheet manufacturing apparatus stores a plating bath containing molten zinc and molten Al at bath temperature T1, and a plating bath for plating a steel plate immersed in the plating bath, and a plating bath transferred from the plating bath, which is lower than T1. By storing in the bath temperature T2 and supersaturating Fe in the plating bath, and maintaining the Al concentration A2 in the bath at a high concentration by the first current diffusion, the top dross is precipitated in the bath, and the top dross is removed. The separation tank for floating separation and the plating bath transferred from the separation tank are stored at a bath temperature T3 higher than T2, so that Fe in the bath is unsaturated, the dross is dissolved, and the Al concentration A3 in the bath is maintained by the second current diffusion. And a circulation section for circulating the plating bath in the order of the plating bath, the separation tank, and the adjustment bath.

Description

Apparatus for producing alloyed hot dip galvanized steel sheet and method for producing alloyed hot dip galvanized steel sheet {APPARATUS FOR PRODUCING ALLOYING GALVANIZED SHEET STEEL AND METHOD FOR PRODUCING ALLOYING GALVANIZED SHEET STEEL}

The present invention relates to an apparatus for producing an alloyed hot dip galvanized steel sheet and a method for producing an alloyed hot dip galvanized steel sheet. In particular, it is related with the alloying hot dip galvanized steel plate manufacturing apparatus and method for making harmless the dross produced at the time of manufacture of an alloy galvanized steel sheet.

This application claims priority based on Japanese Patent Application No. 2010-196797 for which it applied to Japan on September 2, 2010, and uses the content here.

Hot-dip galvanized-aluminum plated steel sheets are used abundantly in the fields of automobiles, home appliances, building materials, and the like. As typical varieties of a plated steel sheet, three kinds of the following are mentioned in order from the thing with small aluminum (Al) content in a plating bath.

(1) alloyed hot dip galvanized steel sheet (bath composition: for example, 0.125 to 0.14 mass% Al-Zn)

(2) Hot-dip galvanized steel sheet (bath composition: 0.15 to 0.25 mass% Al-Zn)

(3) Zinc-aluminum alloy plated steel sheet (bath composition: 2-25 mass% Al-Zn)

As described above, the molten zinc-aluminum plated steel sheet is a steel sheet plated using a plating bath containing a molten metal containing molten zinc and molten aluminum. In this plating bath, aluminum (Al) is added to zinc (Zn), which is a main component, for the purpose of improving plating adhesion and corrosion resistance, and further, for example, a substance such as magnesium (Mg) or silicon (Si) for the purpose of improving corrosion resistance. It may be added.

Hereinafter, the plating bath for manufacturing an alloying hot dip galvanized steel plate "GA" and GA is called "alloying hot dip galvanization bath (GA bath)." The hot dip galvanized steel sheet is referred to as "GI" and the plating bath for producing GI is called "hot dip galvanized bath (GI bath)".

When manufacturing the above-described hot dip galvanized-aluminum plated steel sheet, a large amount of foreign matter called dross is produced in the plating bath. This dross is an intermetallic compound of iron (Fe) melt | dissolved in a plating bath from a steel plate, and Al or Zn contained in a plating bath (molten metal). More specific compositions of this intermetallic compound are, for example, top dross represented by Fe ₂ Al ₅ and bottom dross represented by FeZn ₇ . The top dross may be produced in all plating baths (eg, GA baths and GI baths) for manufacturing the zinc-aluminum-based hot dip galvanized steel sheet, while the bottom dross is an alloyed hot dip galvanizing bath (GA bath). Is generated only).

Since the top dross has a specific gravity smaller than the molten metal forming the plating bath, the top dross floats in the plating bath and finally floats in the bath surface. If the number of the top dross floating in the plating bath is large, the top dross is precipitated on the roll surface in the bath, which causes the scratches to occur in the steel sheet. The floating top dross precipitates in the grooves of the rolls in the bath, thereby lowering the apparent coefficient of friction between the rolls and the steel sheet, thus causing roll slip and failure. Furthermore, when a relatively large diameter top dross adheres to the steel sheet, the appearance quality of the product is reduced, and the grade is degraded depending on the use.

On the other hand, since the specific gravity is larger than the molten metal which forms a plating bath, a bottom dross floats in a plating bath and finally deposits in the plating tank bottom. If the number of bottom dross in the plating bath is large, similar to the top dross, problems such as scratches in the bath, slippage of the roll, failure, and deterioration in appearance quality due to adhesion to the steel sheet occur. In addition, the bottom dross does not float on the bath surface like the top dross, and does not harm it, and the bath dross floats in the bath for a long time, or the bottom dross once deposited on the bottom of the plating bath is floated again in the plating bath due to the change in the flow in the bath. do. For this reason, it can be said that the bottom dross is more harmful than the top dross.

In particular, in order to improve the productivity of the plated steel sheet, when the speed of the plate flow rate of the steel sheet immersed in the plating bath is increased, the bottom dross deposited on the bottom of the plating bath is bathed by the bath flow accompanying the high speed movement of the steel sheet. Dried up in the middle Since the dross adheres to the steel sheet and generates dross scratches, the dross becomes a factor of deterioration of the quality of the coated steel sheet. Therefore, conventionally, in order to ensure the quality of a plated steel plate, the plate | board speed | rate of a steel plate was restrained and productivity had to be sacrificed.

Many proposals have been made in the past to solve the problems caused by the top dross and the bottom dross as described above. As shown below, these proposals generally have a method of sedimentation separation or flotation separation using the specific gravity difference between the plating bath and the dross.

For example, Patent Document 1 proposes a dross removal apparatus for guiding a zinc bath containing dross from a plating bath to a storage tank, and floating and sedimenting the dross using a specific gravity difference between the dross and the plating bath. It is. In this apparatus, the capacity of the storage tank is 10 m 3 or more, the transfer amount of the zinc bath is 2 m 3 / h or more, and a blocking plate for bypassing the bath is provided in the storage tank. However, in patent document 1, the formula which holds | maintains in the sedimentation removal of particle | grains in the case of relatively slow bath flow is employ | adopted, and the dross removal effect is evaluated excessively. In addition, although the patent document 1 prescribes a harmful dross to 100 micrometers or more, the dross | scratches which are currently a problem include the flaw which causes dross about 50 micrometers of dross diameters. In practice, countermeasures having a greater effect than Patent Document 1 are necessary. By the way, in the method of patent document 1, when a 50 micrometer dross is made into object to remove, since a storage tank of 42 m <3> or more is needed, enlargement of an apparatus cannot be avoided and it is not practical. In addition, in order to downsize the apparatus, since the sedimentation speed of the bottom dross is slow, measures other than Patent Document 1 are necessary.

Patent Literature 2 proposes a plating apparatus that prevents curling of a bottom dross by providing an enveloping member in a plating tank and by setting down and depositing a bottom dross on a lower side of the enveloping member. However, in the method of this patent document 2, since the bath in the upper area | region of a plating bath becomes violent with the raise of a plating rate, the bath in the lower area | region also becomes quick too. For this reason, since the small diameter dross is refluxed in the upper region by bathing without sedimentation, the dross removal efficiency is low. In addition, in the case of a realistic plating bath capacity (for example, 200t), the small diameter dross grows with the passage of time while refluxing in the upper region and the lower region of the plating bath, and eventually settles in the lower region. However, at that time, since the bottom dross which grew to the diameter which can be precipitated is floating in a large amount in the upper area | region and the lower area | region of a plating bath, it is low effect as a countermeasure for dross scratches. Further, the bottom dross deposited in the lower region needs to be removed at some time, but the dross removal operation is practically impossible with the enclosing member. In order to remove an enclosure member, since considerable effort and time are required, it can be said that the technique of patent document 2 is not practical.

In the apparatus proposed by patent document 3, a plating container is divided into a plating tank and a dross removal tank, and the molten metal in a plating tank is conveyed to a dross removal tank by a pump. The dross removal tank settles and removes the dross, and the cleaned bath is refluxed into the plating tank from the opening provided in the plating tank. However, in the method described in this Patent Document 3, since the dross is separated using only the specific gravity difference between the bath and the bottom dross, the separation efficiency of the small diameter dross is low, and the reflux is carried back to the plating bath through the bath. In addition, when the realistic dross removal tank capacity (for example, 200t) is used, the small diameter dross produced in the plating tank grows with the passage of time while circulating the plating bath and the dross separation tank in a bath, Eventually it settles in the dross removal tank. However, in that case, since the bottom dross which grown to the diameter which can be precipitated is floating in a large amount in a plating tank and a dross removal tank, it can be said that the technique of patent document 3 is ineffective as a countermeasure for dross scratches.

In addition, the plating apparatus proposed in patent document 4 guides the plating bath in a plating pot to a dross crystal tube, and repeats cooling and heating with respect to a plating bath in a dross crystal tube. As a result, the dross is grown and removed, and the cleaned plating bath is reheated in the reheating bath and then returned to the plating bath. In addition, in the plating method proposed in patent document 5, a sub port is provided separately from a plating port. The molten metal containing the bottom dross is transferred from the plating port to the sub port, the bath in the sub port is maintained at a higher temperature than the plating port, and the Al concentration is increased to 0.14 mass% or more. As a result, the bottom dross contained in the plating bath is transformed into the top dross to be floated and removed.

Japanese Patent Application Laid-open No. Hei 10-140309 Japanese Patent Application Publication No. 2003-193212 Japanese Patent Application Publication No. 2008-095207 Japanese Patent Application Laid-Open No. 05-295507 Japanese Patent Application Laid-Open No. 04-99258

As described above, in the conventional dross removing method described in Patent Documents 1 to 3, sedimentation separation or flotation separation is performed by using only the specific gravity difference between the dross and the plating bath without performing bath temperature control of the plating bath. The method was common. However, in such a removal method, since the small diameter dross is refluxed in a plating bath via a bath, the dross cannot be removed completely and there is a problem that the removal efficiency of the dross is low. Further, the small diameter dross in the plating bath grows with the passage of time while circulating through the bath between the separation tank and the plating bath, and eventually precipitates in the separation bath. However, at this time, since the dross which grew to the diameter which can be settled is floating in a large amount in a plating bath, the effect as a countermeasure for the dross scratch of a plated steel plate was low.

On the other hand, in the method described in Patent Document 4, the molten metal in the plating bath is transferred into the dross crystallization tube, and the dross is grown and removed by repeating the cooling and heating for the plating bath a plurality of times. By the way, in order to utilize the method of this patent document 4 effectively, as described in the Example of patent document 4, the circulation amount of a plating bath shall be 0.5 m <3> / min (about 200 t / h), need. In order to continuously perform cooling and heating for 2 hours as described in the above example, the plating bath of such a large flow rate, a dross crystallization tube having an internal volume of 60 m 3 (about 400 t), a large-capacity cooling device, and heating The device is needed. In addition, Patent Document 4 does not specify a method for removing the dross grown in the dross crystal tube. In the case of removing the dross using a filter, the replacement operation is practically impossible, and in the case of removing the dross by sedimentation separation, a sedimentation tank for it is required separately, but in principle, it is practically possible. Is difficult to operate. Therefore, it can be said that the method of patent document 4 is not realistic.

In addition, the method described in Patent Literature 5 maintains the bath temperature of the plating bath in the sub-port at a higher temperature than the plating port, and increases the Al concentration to transform the bottom dross included in the plating bath into a top dross to remove the injury. It is. As described in the Example of patent document 5, the plating bath (bath temperature 460 degreeC, Al density | concentration 0.1 mass%) in a plating pot is heated up at bath temperature 500 degreeC and 550 degreeC in a sub pot, and Al concentration is made into 0.15 mass%. Under elevated conditions, a portion of the bottom dross may be transformed into a top dross so that it can be separated. However, in this method, since the solubility limit of Fe in the plating bath is drastically increased (saturated Fe concentration of the plating port bath: 0.03 mass%, saturated Fe concentration of the subport bath: 0.09 mass% or more), most of the dross It will be dissolved in the silver plating bath. In other words, if the bath temperature of the plating bath is increased in the sub-port, the dissolution limit of Fe in the plating bath increases, so that most of the dross is dissolved in the plating bath, so that the dross can be separated from the sub-port by floating. none. Therefore, when the plating bath in the sub-port is lowered and returned to the plating port, a large amount of dross is generated due to the solubility difference of Fe. Thus, the method of patent document 5 has a big question about the dross removal effect in reality. Moreover, in the method of patent document 5, after the dross removal process in a sub port, a plating bath is cooled to the bath temperature of a plating port in the said sub port, and the said plating bath is collect | recovered. Therefore, the dross removal processing in the sub-port is inevitably a batch process, so that the dross removal performance is inferior as compared with the case of performing the dross removal processing continuously.

As mentioned above, the method of removing the dross floating in a plating bath has been examined for a long time, and most of them were the separation method using the specific gravity difference of a dross and a plating bath (refer patent documents 1-3). Among these, in the method of sedimenting and separating the bottom dross, since the specific gravity difference between the bottom dross and the zinc bath is small, the sedimentation speed of the bottom dross is slow, and the dross is almost completely harmless at a realistic separation tank capacity. Free) was difficult.

On the other hand, the method of floating separation of the top dross is advantageous over the method of sedimentation separation of the bottom dross. However, under normal GA operating conditions, since dross is generated only in the bottom dross or in a mixed state of the bottom dross and the top dross, a method of transforming the bottom dross into the top dross is required. Some examples are mentioned as this means (for example, refer patent document 5).

However, as mentioned above, the conventional dross removal method proposed so far is not practical because it is difficult to control Al concentration in a bath, or there is technical difficulty in the technical thought. These conventional methods have had insufficient dross removal performance and effects, or have a big question about the dross removal effect itself.

This invention is made | formed in view of the said problem, The objective is that the dross which inevitably arises in a plating bath at the time of manufacture of an alloying hot dip galvanized steel plate can be removed efficiently and effectively, and can be almost completely harmless. And a novel and improved alloyed hot dip galvanized steel sheet production apparatus and a method for producing an alloyed hot dip galvanized steel sheet.

In light of the above circumstances, the inventors of the present invention have found a method of effectively and efficiently removing dross and making the dross almost completely harmless (dross free) in the system. In this method, the plating bath is circulated between three divided tanks, that is, the plating tank, the separation tank, and the adjustment tank, and (1) the resulting dross in the plating bath is precipitated as a top dross in the separation tank having a lower bath temperature than the plating tank. And (2) combining the step of dissolving and removing the top dross which is not completely separated and removed in the separation tank by using Fe in the plating bath in an unsaturated state in the adjustment tank having a higher bath temperature than the separation tank. .

In order to achieve the said objective, each aspect of this invention has the following structures.

(a) The alloying hot dip galvanized steel sheet manufacturing apparatus which concerns on 1 aspect of this invention has a 1st heat insulating part which heat-insulates the plating bath which is a molten metal containing molten zinc and molten aluminum at predetermined | prescribed bath temperature T1, and is in the said plating bath. A plating bath for plating the immersed steel plate, and a second heat insulating part for insulating the plating bath transferred from the plating bath outlet of the plating bath at a bath temperature T2 lower than the bath temperature T1, and the aluminum concentration A1 in the plating bath in the plating bath. Floating top dross which precipitated by making aluminum concentration A2 in the said plating bath conveyed from the said plating bath into 0.14 mass% or more by the replenishment of the first zinc containing omega containing higher concentration aluminum than And a third thermal insulation portion for insulating the plating bath transferred from the separation tank to a bath temperature T3 higher than the bath temperature T2, wherein the aluminum The aluminum concentration A3 in the plating bath conveyed from the separation tank is now higher than the aluminum concentration A1 by the replenishment of the second zinc-containing now containing aluminum having a lower concentration than that of FIG. A2 or no aluminum. An adjustment tank for adjusting to a concentration lower than aluminum concentration A2, and a circulation section for circulating the plating bath in the order of the plating tank, the separation tank, and the adjustment tank.

(b) In the apparatus for producing an alloyed hot dip galvanized steel sheet according to (a), further comprising an aluminum concentration measuring unit for measuring the aluminum concentration A1 in the plating bath in the plating bath, wherein the circulation unit measures the aluminum concentration measuring unit. According to a result, you may control the circulation amount of the said plating bath.

(c) In the alloying hot dip galvanized steel sheet manufacturing apparatus of (a), the second heat insulating part such that the bath temperature T2 of the separation bath is 5 ° C or more lower than the bath temperature T1 of the plating bath and is equal to or higher than the melting point of the molten metal. It may be controlled by.

(d) In the alloying hot-dip galvanized steel sheet manufacturing apparatus of (a) above, when the bath temperature drop width of the plating bath at the time of transferring from the adjusting bath to the plating bath is ΔT _fall in degrees Celsius, the bath temperature T1 and the bath temperature T2 And the bath temperature T3 may be controlled by the third thermal insulation unit so that the bath temperature T3 satisfies the following expressions (1) and (2) at the Celsius temperature.

(e) In the apparatus for producing an alloyed hot dip galvanized steel sheet according to the above (a), the molten metal of the second zinc-containing present molten metal further provided with a premelt bath for melting the second zinc-containing present invention. This may be supplied to the plating bath in the adjustment tank.

(f) In the alloying hot dip galvanized steel sheet manufacturing apparatus of said (a), the said circulation part may be equipped with the molten metal transfer apparatus provided in at least one of the said plating tank, the said separation tank, or the said adjustment tank.

(g) In the alloying hot dip galvanized steel sheet manufacturing apparatus of (a), the plating bath of the plating bath so that the plating bath flows out from the upper portion of the plating bath by the flow of the plating bath accompanying the running of the steel plate. The exit may be located downstream of the traveling direction of the steel sheet.

(h) In the apparatus for producing an alloyed hot dip galvanized steel sheet according to the above (a), at least two of the plating bath, the separation bath, or the adjustment bath are configured by partitioning one tank by a weir, and divided by the weir. Bath temperature of each group may be controlled independently.

(i) In the alloying hot-dip galvanized steel sheet manufacturing apparatus of said (a), the storage amount of the said plating bath in the said plating tank may be 5 times or less of the circulation amount of the said plating bath per hour by the said circulation part.

(j) In the alloying hot-dip galvanized steel sheet manufacturing apparatus of (a) above, the storage amount of the plating bath in the separation tank may be twice or more the circulation amount of the plating bath per hour by the circulation section.

(k) The alloying hot dip galvanized steel sheet manufacturing method according to one embodiment of the present invention is the plating bath while circulating a plating bath that is a molten metal containing molten zinc and molten aluminum in the order of a plating bath, a separation tank, and an adjustment tank. The plating bath transferred from the adjustment tank is stored at a predetermined bath temperature T1 to plate the steel plate immersed in the plating bath, and in the separation tank, the plating bath transferred from the plating bath to the separation tank, In the plating bath transferred from the plating bath by the first zinc-containing current supply which is stored at the bath temperature T2 lower than the bath temperature T1 of the plating bath and contains aluminum at a higher concentration than the aluminum concentration A1 in the plating bath in the plating bath. The aluminum dross A2 is 0.14 mass% or more, the precipitated top dross is separated by levitation, and transferred from the separation tank in the adjustment tank. The pre-plating bath is stored at a bath temperature T3 higher than the bath temperature T2 of the separation tank, and by the current diffusion of a second zinc-containing containing or containing aluminum at a lower concentration than the aluminum concentration A2 in the plating bath of the separation tank. The aluminum concentration A3 in the plating bath transferred from the separation tank is adjusted to a concentration higher than the aluminum concentration A1 and lower than the aluminum concentration A2.

According to the alloying hot dip galvanized steel sheet manufacturing apparatus and method as described in said (a) and (k), a plating bath is circulated in order of a plating tank, a separation tank, and an adjustment tank. Thereby, in the said plating tank, since the residence time of a circulation bath can be shortened, dross can generate | occur | produce in a plating tank and growth to a noxious diameter can be avoided. Subsequently, in the separation tank, Fe is made into a supersaturated state by lowering the bath temperature of the circulation bath, thereby precipitating Fe in the bath as a top dross, and transforming a harmless diameter bottom dross contained in the inlet bath into a top dross. , Can separate the injury. In addition, in the said adjustment tank, when Fe in a plating bath is made into the unsaturated state by the bath temperature rise of a circulation bath, the small diameter top dross which was not completely removed and removed from a separation tank is melt | dissolved and removed by the current replenishment, The composition of the plating bath transferred from the adjustment tank to the plating tank can be adjusted.

According to the invention of (a) and (k), the production and growth of dross in the plating bath is suppressed, the top dross is separated and removed in the separation tank, and the residual dross is dissolved in the adjustment tank. For this reason, the dross which inevitably arises in a plating bath can be made almost completely harmless.

According to the invention of the above (b), the Al concentration in the bath of the plating bath stored in the separation tank can be increased to the concentration necessary for making the top dross generating region. For this reason, the produced dross in a separation tank can be made into only the top dross.

According to the invention of (c), the Fe dissolution limit of the plating bath stored in the separation tank is lowered. For this reason, dross equivalent to the amount of Fe supersaturated can be forcibly precipitated.

According to the invention of (d), the bath temperature of the plating bath stored in the adjustment tank is maintained higher than that of the separation tank, and the bath temperature variation of the plating bath in the plating tank is reduced. For this reason, melt | dissolution of residual dross in an adjustment tank and generation | occurrence | production of the noxious diameter dross in a plating tank can be suppressed.

According to the invention of (e) above, there is no need to dissolve the now in the adjusting tank. For this reason, in an adjustment tank, the drastic temperature fall of the molten metal currently accompanying input, and the dross which arises as a cause can be suppressed.

According to the invention of (f), the bath circulation amount of the plating bath circulated in the order of the plating bath, separation tank, and adjustment tank is controlled. Therefore, the composition of the plating bath required for the plating bath of the plating bath and the composition of the plating bath required for the separation bath plating bath can be satisfied at the same time.

According to the invention of (g), it is difficult to form a local retention region of the plating bath 10A in the plating bath 1. For this reason, dross can be prevented from growing to the nominal diameter in the retention area in the plating tank 1.

According to the invention of (h), three or two tanks of the plating bath, the separation bath, and the adjustment bath are integrally formed. For this reason, the device configuration can be simplified.

According to the invention of (i), the residence time of the plating bath in the plating bath is shortened. This allows the dross to flow out from the plating bath to the separation bath before growing to the nominal diameter.

According to the invention of (j), the residence time of the plating bath in the separation tank becomes long. For this reason, top dross can be fully removed from a separation tank.

1 is a ternary state diagram showing a dross generation range in various plating baths.
Fig. 2 is a graph showing the growth of dross in each phase under conditions of constant bath temperature.
It is a schematic diagram explaining the floating state of the dross in a plating tank.
It is a schematic diagram explaining the floating state of the dross in a plating tank.
It is a schematic diagram which shows the structural example 1 of the alloying galvanized steel plate manufacturing apparatus which concerns on one Embodiment of this invention.
FIG. 5: is a schematic diagram which shows the structural example 2 of the alloying hot-dip galvanized steel plate manufacturing apparatus which concerns on the 1st modified example of the said embodiment.
FIG. 6: is a schematic diagram which shows the structural example 3 of the alloying galvanized steel plate manufacturing apparatus which concerns on the 2nd modified example of the said embodiment.
It is a schematic diagram which shows the structural example 4 of the alloying galvanized steel plate manufacturing apparatus which concerns on the 3rd modified example of the said embodiment.
FIG. 8: is a schematic diagram which shows the structural example 5 of the alloying galvanized steel plate manufacturing apparatus which concerns on the 4th modified example of the said embodiment.
It is a schematic diagram which shows the allowable bath temperature range of each tank when the bath temperature of a plating tank which concerns on the said embodiment is 460 degreeC.
10 is a ternary state diagram showing a state transition of the plating bath in each bath according to the embodiment described above.
11 is a ternary state diagram for explaining a state of the GA bath according to the embodiment.
It is a graph which shows the bath conditions for making all the precipitation dross into a top dross in a separation tank concerning the said embodiment.
It is a graph which shows the relationship between the capacity | capacitance of a separation tank, and the dross | separation separation ratio which concerns on the Example of this invention.
14 is a graph showing the relationship between the bath circulation amount and the dross diameter according to the embodiment.
15 is a graph showing a relationship between a bath temperature variation of a plating bath inflow bath and a dross diameter according to the embodiment.

Best Modes for Carrying Out the Invention Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, in this specification and drawing, duplication description is abbreviate | omitted by attaching | subjecting the same number about the component which has substantially the same functional structure.

[One. Review of dross generation and dross removal method]

First, prior to the description of the alloying hot dip galvanized steel sheet production apparatus and the alloying hot dip galvanized steel sheet manufacturing method according to the present embodiment, a factor in which dross (top dross, bottom dross) is generated in the plating bath, Describe the results of the review on how to remove them.

1.1. Dross generation range]

As described above, the molten zinc-aluminum plated steel sheet is a steel sheet plated using a molten metal in which aluminum is added to zinc as a main component. For example, (1) alloying hot dip galvanized steel sheet, (2) hot dip galvanized steel sheet, (3) zinc-aluminum alloy plated steel sheet, etc. are mentioned.

The alloyed hot dip galvanized steel sheet (GA) is a steel sheet in which a molten Zn and a steel are alloyed with a short time heating immediately after hot dip galvanizing to form a Zn-Fe-based intermetallic compound film. The said GA is used abundantly, for example in steel sheets for automobiles. The plating layer of GA includes an alloy of Fe and Zn dissolved in a plating bath from a steel sheet. The composition of the plating bath (GA bath) for producing GA is, for example, 0.125 to 0.14 mass% Al-residual Zn. This GA bath further contains Fe dissolved in the plating bath from the steel sheet. A relatively low concentration of Al is added to the GA bath in order to improve plating adhesion. If the Al concentration in the GA bath is too high, the Al layer of the GA bath is suppressed to a predetermined low concentration of 0.125 to 0.14% by mass because the so-called aluminum barrier makes the plating layer difficult to Fe-Zn alloy.

Hot-dip galvanized steel sheet (GI) is used abundantly in general building materials. The composition of the plating bath (GI bath) for manufacturing GI is 0.15-0.25 mass% Al-residual Zn, for example. By setting the Al concentration of the GI bath to 0.15 to 0.25% by mass, the adhesion of the plating layer to the steel sheet becomes very high, and it is possible to prevent the plating layer from detaching following the deformation of the steel sheet.

A zinc-aluminum alloy plated steel sheet is used abundantly, for example in building materials with high durability requirements. The composition of the plating bath for manufacturing the said steel plate is 5 mass% Al-residual Zn, 11 mass% Al-residual Zn, etc. Since a sufficient amount of Al is contained in the zinc bath, it has higher corrosion resistance than GI.

In the plating bath for producing these hot-dip galvanized-aluminum hot-dip steel sheets, a large amount of top dross and bottom dross which are intermetallic compounds of Fe and Al or Zn dissolved in the bath are produced. The production of dross in the plating bath depends on the temperature (bath temperature) of the plating bath and the solubility of Fe dissolved in the plating bath from the Al concentration and the Fe concentration (steel plate) in the plating bath.

1 is a ternary state diagram showing a dross generation range in the various plating baths. 1, the horizontal axis represents Al concentration (mass%) in the plating bath, and the vertical axis represents Fe concentration (mass%) in the plating bath.

As shown in FIG. 1, when the Fe concentration in the plating bath exceeds a predetermined concentration determined according to the Al concentration, dross is generated. For example, in a GA bath having a bath temperature T of 450 ° C. and an Al concentration of 0.13% by mass, when the Fe concentration in the bath is higher than about 0.025% by mass, bottom dross (FeZn ₇ ) is produced. In addition, in a GA bath having a bath temperature T of 450 ° C. and an Al concentration of 0.14% by mass, when the Fe concentration is higher than about 0.025% by mass, top dross (Fe ₂ Al ₅ ) is formed, and the Fe concentration is further increased. In addition to the top dross, a bottom dross (FeZn ₇ ) is produced. Thus, in the above conditions, the top dross and the bottom dross are mixed.

On the other hand, since the GI bath has a higher Al concentration than the GA bath (for example, 0.15 to 0.25 mass%), the dross produced in the GI bath is only the top dross (Fe ₂ Al ₅ ). For example, in a GI bath in which the bath temperature T is 450 ° C., when the Fe concentration in the bath is higher than about 0.01% by mass, top dross is generated. In addition, although not shown in figure, even if it is a plating bath for zinc-aluminum alloy plated steel sheets, since Al concentration is high enough (for example, 2-25 mass%), only a top dross is produced | generated.

As can be seen from FIG. 1, even in the same plating bath, the higher the bath temperature T, the higher the lower limit of the Fe concentration at which dross is produced. For example, in a GA bath having an Al concentration of 0.13% by mass, the conditions under which bottom dross is produced are as follows: (1) When the bath temperature T is 450 ° C, the Fe concentration is about 0.025% by mass or more, and (2) the bath temperature. Fe concentration is about 0.035 mass% or more when T is 465 degreeC, and (3) Fe concentration is about 0.055 mass% or more when bath temperature T is 480 degreeC. Therefore, when Fe concentration in a bath is constant (for example, 0.03 mass% Fe), when bath temperature T is raised from 450 degreeC to 465 degreeC, Fe will become unsaturated from supersaturated state, and a bottom dross will melt | dissolve in a bath and lose | disappears Will be. On the contrary, when bath temperature T is reduced from 465 degreeC to 450 degreeC, Fe will become supersaturated from unsaturated state, and a bottom dross will produce | generate.

1.2. Dross generation factor]

Next, the generation factor of dross in a plating bath is demonstrated. As a generation factor of dross, the following factors (1)-(3) are considered, for example. Each factor is demonstrated below.

(1) Melting Now for Plating Baths

Now, the molten metal consumed for plating the steel sheet in the plating bath is used to replenish the plating bath. The solid now is immersed in a hot plating bath at an appropriate timing during operation, and dissolved in the plating bath to form a liquid molten metal. In the case of hot-dip galvanizing, zinc containing now containing at least Zn is used, but the said zinc containing now contains metals, such as Al, in addition to Zn according to the composition of a plating bath. Although the present melting | fusing point changes with present composition, it is 420 degreeC, for example, and is lower than the bath temperature (for example, 460 degreeC) of a plating bath.

When the now immersed in the plating bath is dissolved, the temperature of the surrounding molten metal is lower than the bath temperature T of the plating bath. That is, a temperature difference arises between the now ambient temperature (for example, 420 degreeC) immersed in a plating bath, and bath temperature T (for example, 460 degreeC) of a plating bath. Therefore, when Fe in the bath is saturated, a large amount of dross is produced relatively easily in the low temperature region around now. The resulting dross phase follows the state diagram (see FIG. 1).

Usually, in a plating bath, since steel plate is always immersed and the active iron surface is exposed, Fe concentration in a bath is in a saturated state. Therefore, in the plating bath in which Fe is saturated, when the temperature of the molten metal around the present abruptly decreases with the current input, the supersaturated Fe reacts with Zn or Al in the bath and dross is produced. do. In addition, in the case of dissolving the present metal in advance using a premelt bath and replenishing the molten metal in the plating bath of the plating bath, in the premelt bath, Fe is unsaturated, so dross is hardly generated.

(2) Fluctuation of plating bath temperature T

Fluctuation of bath temperature T of a plating bath is mentioned as a factor of dross formation following the said now melt | dissolution. When bath temperature T rises, the Fe dissolution limit of a plating bath becomes high, Fe further elutes from the steel plate immersed in a plating bath, and Fe in a plating bath reaches saturation concentration rapidly. When bath temperature T of this plating bath falls, Fe will become supersaturated in all the places of a plating bath, and dross is produced | generated quickly. In addition, even if the bath temperature T of the low-temperature plating bath containing this dross rises again and the Fe dissolution limit is increased, the Fe dissolution rate from the steel sheet is faster than the decomposition (dissipation) of the dross, so that the dross is decomposed (dissipated). There is nothing to be done. That is, in the plating bath in which the steel plate is immersed, it is difficult to lose the dross even if the bath temperature of the low-temperature plating bath (Fe supersaturated state) is raised.

On the other hand, when the low-temperature molten metal containing the dross is transferred to a bath without immersion of the steel sheet, and the temperature is elevated and left for a long time, the plating bath is in an unsaturated Fe state, whereby the dross can be decomposed (dissipated). Therefore, from this viewpoint, in the alloying hot dip galvanized steel sheet manufacturing apparatus which concerns on this embodiment mentioned later, after generating dross in a plating bath in a separation tank, the said plating bath is transferred to the adjustment tank which does not immerse a steel plate, The bath temperature T is raised to dissolve (dissipate) the dross.

(3) other factors

Fluctuations in Al concentration in the plating bath and temperature variations in the plating bath are also factors for generating dross. When the Al concentration in the plating bath is increased, the Fe dissolution limit in the plating bath is lowered, so that top dross (Fe ₂ Al ₅ ), which is an intermetallic compound of Al and Fe, is likely to be produced. Moreover, when the bath flow in a plating tank falls and the stirring force in a plating tank falls, the temperature of the plating bath of a plating tank bottom part will fall, and dross will produce | generate. Thereafter, when the bath flow is restored, dross deposited at the bottom of the plating bath is blown into the plating bath.

[1.3. Separation of specific gravity of dross]

A method is known in which a top dross is separated from a flotation or a bottom dross is separated by using a specific gravity difference between a molten metal forming a plating bath and a dross. Generally, specific gravity of bottom dross is 7000-7200 kg / m <3>, for example, and specific gravity of top dross is 3900-4200 kg / m <3>, for example. On the other hand, the specific gravity of the zinc bath varies somewhat depending on the temperature and Al concentration, but is, for example, 6600 kg / m 3.

Therefore, in the case where the dross is separated by gravity from the zinc bath, the top dross has a large specific gravity difference from the zinc bath, and thus floats relatively easily. Therefore, it is relatively easy to float the top dross off and discharge it out of the system. However, since the bottom dross has almost no specific gravity difference with the zinc bath, in order to settle the bottom dross, a long period of standing is required under low bath flow conditions. In particular, the small diameter bottom dross is difficult to settle. In addition, since the bottom dross is deposited at the bottom of the tank, there is a possibility that it may be rolled up again, and the final out-of-system discharge (the work of raising the bottom dross from the bottom of the tank) is not simple.

Thus, it is difficult to remove dross in a plating tank, especially the bottom dross deposited at the tank bottom. Although various removal methods have been proposed in the past (see Patent Documents 1 to 5), a method for easily separating and removing the dross with high removal efficiency has not yet been proposed.

1.4. Relationship between Bath Temperature Fluctuation and Dross Growth]

2 is a graph showing the growth of dross in each phase under a condition in which the bath temperature is constant. 2 represents time (days) and a vertical axis | shaft is an average particle diameter (micrometer) of dross particle | grains. 2 shows growth of bottom dross (FeZn ₇ ) generated in the GA bath, and top dross (Fe ₂ Al ₅ ) generated in the GA bath and the GI bath.

As shown in FIG. 2, in any phase dross, if conditions, such as bath temperature T, are constant, a growth rate is slow. For example, under conditions of constant bath temperature, the bottom dross (FeZn ₇ ) grows only from about 15 μm to about 20 μm in average particle diameter in 200 hours, and the top dross (Fe ₂ Al ₅ ) averages in 200 hours. It grows only from a particle diameter of 15 micrometers to about 35 micrometers.

Next, with reference to Table 1, the result observed about the dross formation behavior when a bath temperature is reduced is demonstrated. Table 1 shows the dross growth state at the time of cooling three plating baths A-C from which a composition differs from 460 degreeC to 420 degreeC by predetermined cooling rate 10 degreeC / sec.

As shown in Table 1, when the bath temperature T is lowered from 460 ° C to 420 ° C at a cooling rate of 10 ° C / sec, and the Fe in the plating bath is transferred from an unsaturated state to a supersaturated state, the formation and growth of dross The speed is very fast. For example, in 0.13 mass% Al plating bath A (GA bath), bottom dross (FeZn ₇ ) of about 50 micrometers in particle size is produced | generated for only 4 second. In addition, in 0.14 mass% Al plating bath B (GA bath), the bottom dross (FeZn ₇ ) of about 40 micrometers in particle size, and the top dross (Fe ₂ Al ₅ ) of about 10 micrometers in particle size are mixed. In addition, in the plating bath C (GI bath) of 0.18 mass% Al, three top dross (Fe ₂ Al ₅ ) of about 5 micrometers, 10 micrometers, and 25 micrometers of particle size is produced | generated.

As described above, under the condition that the bath temperature T is constant (see FIG. 2), the growth rate of both the bottom dross and the top dross is slow. Therefore, it can be seen that growth of dross in the plating bath can be suppressed as long as the bath temperature T of the plating bath in the plating bath can be kept as constant as possible. On the other hand, when the bath temperature T is lowered, Fe in the bath transitions from the unsaturated state to the supersaturated state, so the growth rate of the dross is very fast (see Table 1). Therefore, the plating bath of the plating bath is transferred to the separation bath, the Al concentration in the plating bath is increased, and the bath temperature T is lowered, thereby forcibly depositing the top dross in the plating bath of the separation bath, thereby efficiently removing the top dross. It becomes possible to separate floating.

1.5. Relationship between Plating Speed and Dross]

3A and 3B are schematic diagrams illustrating a floating state of dross in a GA bath. FIG. 3A shows a state during normal operation in which the plating speed is 150 m / min or less, and FIG. 3B shows a state in which the plating speed is high speed operation (eg, 200 m / min or more).

In a normal GA bath, a bottom dross is produced, and among them, the bottom dross is sedimented and deposited at the bottom of the plating tank in order of large particle size. When the plating speed (sheet plate speed of the steel sheet) is slow, for example, less than 100 m / min, the bottom dross deposited on the bottom of the bath is hardly rolled up by the bath flow. However, when the plating speed is 100 m / min or more, as shown in Fig. 3A, not only the small diameter dross but also the relatively large medium diameter dross among the bottom dross is subjected to the accompanying flow accompanying the steel plate running. It curls up from a tank bottom part and floats in the plating bath of a plating tank. Therefore, when the production amount and deposition amount of dross in a plating tank are large, productivity of a plated steel plate will be impaired. As described above, when the plating speed is 150 m / min or less, mainly small diameter and medium diameter dross are suspended in the bath.

In addition, when the plating speed (for example, 150 m / min or less) currently suppressed in order to ensure productivity is 200 m / min or more, for example, as shown in FIG. 3B, it is related to a particle diameter Without, all bottom dross is rich. In other words, due to the vigorous bath flow accompanying the high-speed mailing plate, the bottom dross cannot be deposited at the bottom of the bath, and even the large diameter dross is suspended in the plating bath. Therefore, it is difficult to speed up the plating speed unless it is possible to achieve almost complete harmlessness (dross free) of the dross in the plating bath.

[1.6. Dross scratches;

The dross scratches are scratches of the plated steel sheet caused by the dross generated in the plating bath, for example, deterioration of the appearance of the coated steel sheet due to the dross attachment, pressure scratches caused by the dross in the roll in the bath, and the like. It includes. Although the diameter of the dross which produces a dross flaw is said to be 100 micrometers-300 micrometers, dross scratches resulting from very small dross with a particle diameter of about 50 micrometers are also observed today. Therefore, in order to prevent the occurrence of such minute dross scratches, dross free in the plating bath is required.

[2. Configuration of Alloying Hot Dipped Galvanized Steel Sheet Manufacturing Equipment]

Next, with reference to FIGS. 4-9, the structure of the alloying galvanized steel plate manufacturing apparatus concerning one Embodiment of this invention is demonstrated. FIG. 4: is a schematic diagram of the alloying galvanized steel plate manufacturing apparatus which concerns on this embodiment, and FIGS. 5-8 is a schematic diagram which shows the 1st-4th modified example of this embodiment, respectively. FIG. 9: is a schematic diagram which shows the allowable bath temperature range of each tank in the case where the bath temperature of the plating bath 10A stored in the plating tank 1 which concerns on this embodiment is 460 degreeC. Hereinafter, T1 and aluminum concentration are called A1 for the bath temperature of the plating bath stored in the plating tank 1. Similarly, the bath temperature of the plating bath stored in the separation tank 2 is called T2 and the aluminum concentration A2, and the bath temperature of the plating bath stored in the adjusting tank 3 is called T3 and aluminum concentration A3.

4-8, the alloying hot dip galvanized steel plate manufacturing apparatus (henceforth a hot dip galvanizing apparatus) which concerns on this embodiment is the plating tank 1 for plating the steel plate 11, and A separation tank 2 for separating the loss and an adjustment tank 3 for adjusting the Al concentration in the plating bath 10 are provided. Moreover, the said hot-dip plating apparatus uses the molten metal (plating bath 10) for plating the steel plate 11 of plating tank 1 → separation tank 2 → adjustment tank 3 → plating tank 1. The circulation part which circulates in order is provided. The plating bath 10 is a molten metal containing at least molten zinc and molten aluminum, for example, the GA bath. Below, each component of the hot-dip plating apparatus which concerns on this embodiment is demonstrated.

[2.1. Configuration of Circulation Part of Plating Bath]

First, the circulation unit will be described. The circulation part is a molten metal conveying apparatus 5 attached to at least one or more of the plating tank 1, the separation tank 2, or the adjustment tank 3, and a flow path of molten metal which connects between these three tanks. For example, the communication pipes 6 and 7, the transfer pipe 8, and the overflow pipe 9 are provided. The molten metal transfer apparatus 5 can be comprised by arbitrary apparatuses as long as it can transfer a molten metal (plating bath 10), For example, a mechanical pump may be sufficient as it and an electromagnetic induction pump may be sufficient as it.

In addition, the molten metal transfer apparatus 5 may be attached to all the tanks of the plating tank 1, the separation tank 2, and the adjustment tank 3, and may be attached to any 2 or 1 tank of these 3 tanks, and may be installed. You may also However, from the viewpoint of simplifying the device configuration, the transfer device 5 is provided in only one place, and the remaining tanks are connected by the communication pipes 6 and 7, the transfer pipe 8, the overflow pipe 9, and the like. It is desirable to distribute the molten metal between the three baths. In the example of FIGS. 4-8, as the molten metal transfer apparatus 5, the mechanical pump which delivers the said molten metal is provided in the transfer pipe 8 which is a flow path between the plating tank 1 and the adjustment tank 3, and have. As described later, the plating bath transferred from the adjusting tank 3 to the plating bath is a clean plating bath in which dross is almost removed. Thus, by using only the molten metal transfer apparatus 5 only in a clean plating bath, it becomes possible to minimize the malfunction, such as clogging of the dross of the molten metal transfer apparatus 5.

Thus, in this embodiment, in order to circulate the plating bath 10 between the plating tank 1, the separation tank 2, and the adjustment tank 3, the communication pipes 6 and 7, the transfer pipe 8, and the over Pipes, such as the flow pipe 9, are used to communicate between the plating tank 1, the separation tank 2, and the adjustment tank 3 with each other. As described above, when the pipe is used for the circulation of the bath, it is preferable to suppress the erosion of the inner wall of the pipe due to the flow of the bath, to prevent the temperature drop or the solidification of the bath in the pipe, and the like. For this purpose, it is preferable to employ a double pipe in which ceramics are applied in the pipe, and to further insulate or heat the outer wall of the pipe. In particular, before the start of the bath circulation, it is preferable to preheat the pipe to prevent solidification of the bath in the pipe.

[2.2. Joe's entire structure]

Next, the whole structural example of the plating tank 1, the separation tank 2, and the adjustment tank 3 is demonstrated in detail. As shown to FIG. 4, FIG. 5 (1st modification), and FIG. 8 (4th modification), the plating tank 1, the separation tank 2, and the adjustment tank 3 may be independent tank structure, respectively. . For example, in the structure shown in FIG. 4, the plating tank 1, the separation tank 2, and the adjustment tank 3 are arranged side by side in the horizontal direction, and the upper part of the plating tank 1 and the separation tank 2 is communicating pipe | tube. (6), the lower part of the separation tank (2) and the adjustment tank (3) is communicated by the communication tube (7), the adjustment tank (3) and the plating tank (1), the molten metal transfer device (5) It communicates with the transfer pipe 8 provided. Thus, the height of the hot water surface of each bath plating bath is made the same, the plating bath is circulated using piping, such as a communication pipe, and the molten metal transfer apparatus 5 is used only in the lowermost part, The overall configuration can be simplified. In addition, in the structure of the 1st modification shown in FIG. 5, the overflow pipe 9 is provided in the upper side of the plating tank 1 side wall, and the plating bath 10A which overflowed from the plating tank 1 is It flows down into the separation tank 2 through the overflow pipe 9.

In addition, the plating tank 1, the separation tank 2, and the adjustment tank 3 should just be functionally independent. For example, as in the third modified example shown in FIG. 7, the relatively large single tank is divided into three regions by two weirs 21 and 22, whereby the plating bath 1 and the separation tank ( 2) The adjustment tank 3 may be configured, and three tanks may be integrated in appearance. Alternatively, as in the second modified example shown in FIG. 6, the separation tank 2 and the adjustment tank 3 are formed by dividing a single tank into two regions by one weir 23. It is good also as a tank structure which integrated the tank 2 and the adjustment tank 3, and made only the plating tank 1 independent. In this way, the apparatus configuration can be simplified by integrating three or two groups of the plating tank 1, the separation tank 2, and the adjustment tank 3 together.

However, in order to realize the characteristic dross removal method mentioned later, in each tank structure of the said FIG. 4 thru | or 8, it is necessary to control bath temperature and Al concentration in a bath independently in each tank. Specifically, bath temperature T1 and Al concentration A1 in a bath are controlled by the plating tank 1, bath temperature T2 and Al concentration A2 in a bath are controlled by the separation tank 2, and bath temperature T3 and in bath are controlled by the adjustment tank 3 The Al concentration A3 is controlled. For this reason, in each of the plating tank 1, the separation tank 2, and the adjustment tank 3, the heat insulation part 1, the heat insulation part 2, and the heat insulation part which are not shown in order to control the bath temperature T1, T2, T3 of the plating bath to store | store are stored. 3 is installed. The said heat insulation part is equipped with a heating apparatus and a bath temperature control apparatus. The said heating apparatus heats each bath plating bath, and the said bath temperature control apparatus controls the operation | movement of the said heating apparatus. Thus, by the heat retaining part 1, the heat retaining part 2, and the heat retaining part 3, the bath temperature of the plating tank 1, the separation tank 2, and the adjustment tank 3 is hold | maintained at preset temperature T1, T2, T3, respectively. Controlled. In addition, in order to independently control the Al concentration in the bath of each tank, although the sample for aluminum concentration measurement of each tank may be taken regularly by a human hand, it is preferable that each tank is equipped with each aluminum concentration measurement part. The said aluminum concentration measuring part is comprised by the collection apparatus of the sample for aluminum concentration measurement, the aluminum concentration sensor for molten metal, or an alloy. The aluminum concentration of the sample collected by the sampling device may be regularly measured by a chemical analyzer, or the aluminum concentration of the plating bath may be continuously measured using an aluminum concentration sensor. Based on this aluminum measurement result, adjustment of the amount of bath circulation and the addition of the 1st and 2nd zinc containing now is performed, and the Al density | concentration in the bath of each tank is controlled independently.

In addition, in any of the above-described examples of FIGS. 4 to 8, the communication tube 6, the overflow tube 9, and the weir part which are the upper part of the plating bath 1 and are disposed downstream of the traveling direction of the steel plate 11. From the plating bath outlet formed by 21, the plating bath 10A flows out and flows into the separation tank 2. This circulates all the plating baths 10A without generating retention of the plating bath 10A in the plating bath 1 using the flow of the plating bath 10A accompanying the running of the steel plate 11. There is an effect to be able to do it. 4 to 8, the communication tube 7 and the weirs 22 and 23 are arranged so that the plating bath 10B flowing out from the bottom of the separation tank 2 flows into the adjustment tank 3. have. As will be described later, in the separation tank 2, the top dross contains the top dross at a higher density than the bottom of the plating bath 10B of the separation tank 2 in order to float and separate the top dross. Therefore, by transferring the plating bath 10B of the bottom part of the separation tank 2 to the adjustment tank 3, the plating bath 10B of the bottom part with low content of a top dross can be transferred to the adjustment tank 3, Loss removal efficiency becomes high.

[2.3. Composition of Each Group]

Next, the structure of each tank of the plating tank 1, the separation tank 2, and the adjustment tank 3 is demonstrated.

(1) plating bath

First, the plating tank 1 is demonstrated. 4 to 8, the plating bath 1 stores (a) the plating bath 10A containing the molten metal at a predetermined bath temperature T1, and (b) the plating bath 10A. It has a function to plate the steel plate 11 immersed in the middle. The plating bath 1 is a bath for actually immersing the steel plate 11 in the plating bath 10A to plate the molten metal on the steel plate 11. The composition of the plating bath 10A of the plating bath 1 and the bath temperature T1 are maintained in an appropriate range depending on the type of the plated steel sheet to be manufactured. For example, when the plating bath 10 is a GA bath, as shown in FIG. 9, the bath temperature T1 of the plating bath 1 is hold | maintained about 460 degreeC by the heat retention part 1.

In 10 A of plating baths of the plating bath 1, the roll is arrange | positioned in baths, such as the sink roll 12 and a support roll (not shown), and the gas wiping nozzle above the said plating bath 1 is carried out. (13) is arrange | positioned. The strip-shaped steel sheet 11 to be plated enters the inclined downward direction in the plating bath 10A of the plating bath 1, and the advancing direction is changed by the sink roll 12, and is vertically upward from the plating bath 10A. The excess molten metal on the surface of the steel sheet 11 is removed by the gas wiping nozzle 13.

In addition, the storage amount of the plating bath 10A in the plating bath 1 (capacity of the plating bath 1) Q1 [t] is the circulation amount q [t / of the plating bath 10 per hour by the circulation portion. It is preferable that it is 5 times or less of h]. When the storage amount Q1 of the plating bath 10A is larger than five times the circulation amount q, the residence time of the plating bath 10A in the plating bath 1 becomes long, so that dross is generated and formed in the plating bath 10A. It is likely to grow. Therefore, the retention time of the plating bath 10A in the plating bath 1 can be shortened to predetermined time or less by setting the storage amount Q1 of the plating bath 10A to 5 times or less of the circulation amount q. Under these conditions, even if Fe is dissolved from the steel plate 11 in the plating bath 10A of the plating bath 1, no dross is generated in the plating bath 10A, or if dross is formed, for example, it grows to a harmful particle size. Before the above, the plating bath 10A including the dross flows out into the separation tank 2. However, depending on the shape of the plating tank 1, since the retention of the plating bath 10A may occur in the tank, and dross may become harmful in this retention portion, the capacity Q1 of the plating tank 1 is possible. One smaller one is preferred.

During the hot dip operation, a part of the plating bath 10A in the plating bath 1 is always separated from the plating bath outlet formed by the communication tube 6, the overflow tube 9, and the weir 21. 2) outflow. And a part of plating bath 10C flows into plating tank 1 through the transfer pipe 8 etc. from adjustment tank 3 mentioned later. Plate the place where this plating bath 10C flows into the plating tank 1, the upstream side of the steel plate 11, and the place of the plating bath outlet where the plating bath 10A flows out into the separation tank 2. It is preferable to arrange | position the upper part of the tank 1, and downstream of the traveling direction of the steel plate 11. As shown in FIG. This makes it difficult to form a local retention region of the plating bath 10A in the plating bath 1. Therefore, it is possible to prevent the dross from growing to the nominal diameter in the local retention region in the plating bath 1. Here, the traveling direction upstream side of the steel plate 11 is the steel plate 11 at the time of dividing into the longitudinal direction so that the intrusion location of the steel plate 11 in the plating tank 1, and an impression point may be divided. It is the side including the invasion point of the. The traveling direction downstream side of the steel plate 11 is a side including the pulling point of the steel plate 11 in the case where the plating tank 1 is divided into 2 parts.

(2) separation tank

Next, the separating tank 2 will be described. As shown in FIG. 4 thru | or 8, the separation tank 2 is (a) bath temperature of the plating bath 10A of the plating bath 1 which uses the plating bath 10B conveyed from the said plating bath 1 (B) by supersaturating Fe in the plating bath 10B and raising the Al concentration in the bath so that the state (bath temperature and composition) of the plating bath becomes the top dross generating region. Only the top dross is precipitated, and (c) has the function of removing the precipitated top dross by floating separation.

For example, when the plating bath 10 is a GA bath, as shown in FIG. 9, the bath temperature T2 of the separation tank 2 is 5 degreeC than bath temperature T1 of the plating tank 1 by the heat retention part 2. The temperature is kept at a temperature lower than the melting temperature M (for example, melting point of the GA bath 420 ° C) of the molten metal forming the plating bath 10 (eg, 420 ° C ≤ T2 ≤ T1-5 ° C). In addition, Al concentration A2 of the separation tank 2 is adjusted to higher concentration than Al concentration A1 of the plating tank 1. In this manner, the plating bath 10 is transferred from the plating bath 1 to the separation bath 2, the bath temperature T2 is lowered, and the Al concentration A2 is increased to thereby separate the plating bath ( It is possible to forcibly deposit only the top dross without depositing the bottom dross in 10B). For this reason, the said top dross can be removed suitably by floating separation using specific gravity difference.

This principle is explained in more detail. In 10 A of plating baths which flow into the separation tank 2 from the plating tank 1, Fe melt | dissolved from the steel plate 11 is contained. The Fe melt | dissolution limit of the said plating bath falls with fall (T1-> T2) of bath temperature T. For this reason, in the plating bath 10B of the separation tank 2, Fe becomes a supersaturated state and dross corresponding to the amount of Fe which became the said supersaturation precipitates. At this time, in order to make the dross precipitated only as a top dross, it is necessary to make Al density | concentration A2 of the separation tank 2 into high concentration at least 0.14 mass% or more (refer FIG. 1).

Therefore, when manufacturing an alloying hot dip galvanized steel plate GA in comparatively low Al concentration, the high Al concentration now (corresponding to 1st zinc containing now) is thrown into the separation tank 2, and it melt | dissolves. This high Al concentration Now, Al and zinc are higher than Al concentration A1 (for example, 0.135 mass% Al) of the plating tank 1. By this current supply of high Al concentration, the Al concentration A2 of the separation tank 2 can be maintained at least 0.14% by mass or more in which the state of the plating bath 10B becomes the generation region of the top dross. At this time, in the plating bath 10B of the separation tank 2, only the top dross is precipitated, and the bottom dross is not precipitated. (10)] is smaller than the specific gravity. Therefore, in the separation tank 2, the top dross can be lifted and separated appropriately and can be easily removed.

In addition, the bath temperature T2 of the separation tank 2 is lowered than the bath temperature T1 of the plating tank 1 in order to make Fe in the bath supersaturated, and the bath temperature T2 of the separation tank 2 is equal to or higher than the melting point M of the molten metal. This is to avoid solidification of the plating bath 10B.

As described above, in the separation tank 2, a large amount of top dross is forcibly generated in the plating bath 10B by the decrease in the bath temperature T of the plating bath 10 and the increase in the Al concentration. The top dross floats in the plating bath 10B due to the specific gravity difference with the plating bath 10B and is captured by the bath surface. However, some time is required for the separation of the top dross. Therefore, the storage amount (capacity of the separation tank 2) Q2 [t] of the plating bath 10B in the separation tank 2 is the circulation amount q [t / h of the plating bath 10 per hour by the circulation portion. It is preferable that it is 2 times or more of]. Thereby, since the plating bath 10 flows into the separation tank 2 from the plating tank 1, and flows out to the adjustment tank 3, floating separation time of 2 hours or more on average can be obtained, and therefore, the separation tank 2 The top dross can be sufficiently removed. On the other hand, when the storage amount Q2 of the plating bath 10B in the separation tank 2 is less than twice the circulation amount q of the plating bath 10 per hour, the floating separation time of the top dross cannot be sufficiently obtained. The removal efficiency of the top dross decreases.

In addition, during the hot dip operation, a part of the plating bath 10A flows into the separation tank 2 through the communication tube 6, the overflow tube 9, and the like from the plating bath 1 at the same time. A part of the plating bath 10B in (2) flows out into the adjustment tank 3 through the communication pipe 7 etc.

(3) adjustment tank

Next, the adjustment tank 3 is demonstrated. As shown to FIG. 4 thru | or 8, the adjustment tank 3 is (a) bath temperature T1 of the plating tank 1, and the separation tank 2 of the plating bath 10C conveyed from the said separation tank 2 Is stored at bath temperature T3 higher than bath temperature T2, (b) Fe in the plating bath 10C is unsaturated, and the dross contained in the plating bath 10C is dissolved, and (c) plating bath 1 In order to keep constant the bath temperature T1 and Al concentration A1, it has a function of adjusting the bath temperature T3 and Al concentration A3 of the plating bath 10C conveyed to the plating tank 1. At this time, Al concentration A3 in the bath of the adjustment tank 3 is higher than Al concentration A1 (for example, 0.125-0.14 mass%) in the bath of the plating tank 1, and Al concentration in the bath of the separation tank 2 is carried out. It adjusts to concentration lower than A2 (for example, 0.147 mass%).

This adjustment tank 3 is a tank in which a low Al concentration current (corresponding to the second zinc-containing current) for replenishing the molten metal consumed in the plating tank 1 is injected and dissolved. The adjustment tank 3 regenerates the bath temperature T lowered in the separation tank 2, and further reduces and optimizes the Al concentration in the bath when the separation tank 2 increases the Al concentration A2 in the bath. It also has a role.

In the adjusting tank 3, in order to lower the Al concentration in the bath of the plating bath 10, the second zinc-containing now contains Al having a lower concentration than Al concentration A2 in the plating bath 10B of the separating bath 2. What is necessary is just to introduce | transduce and melt | dissolve the zinc containing now, or the zinc containing now, which does not contain Al, in 10 A of plating baths of the adjustment tank 3. This low Al concentration can now optimize the Al concentration A3 of the plating bath 10C transferred from the adjustment tank 3 to the plating tank 1 (A2 &gt; A3 &gt; A1). The Al concentration A1 of the plating bath 10A can be maintained at a constant appropriate concentration suitable for the composition of the desired GA bath. For example, in the GA bath, Al concentration A1 of the plating bath 10A of the plating bath 1 can be maintained at a constant concentration within the range of 0.125 to 0.14 mass%.

In addition, it is necessary for the bath temperature T3 of the adjustment tank 3 to be a temperature range which does not become a problem even if the said plating bath 10C flows into the plating tank 1 by the heat retention part 3. Therefore, as shown in FIG. 9, it is preferable that the bath temperature T3 of the adjustment tank 3 becomes a temperature difference within +/- 10 _degreeC from the temperature which added bath temperature _fall width ΔT _fall to bath temperature T1 of the plating tank 1 (T1 + ΔT). _fall −10 ° C. ≦ T 3 ≦ T 1 + ΔT _fall + 10 ° C.). Here, the bath temperature drop width ΔT _fall is a bath temperature drop width of the plating bath 10C that occurs naturally when the plating bath 10C is transferred from the adjustment tank 3 to the plating bath 1. When the bath temperature T3 of the adjustment tank 3 is out of the said temperature range, the bath temperature distribution in the plating tank 1 will become large, and dross generation and growth in the plating tank 1 will be encouraged. In addition, the bath temperature T4 of the plating bath 10C in the inlet of the plating tank 1 is in the range of +/- 10 degreeC with respect to the bath temperature T1 of the plating bath 1 (T1-10 degreeC <= T4 <= T1 + 10 degreeC) .

In addition, in order to dissolve the residual dross of the small diameter which was not completely removed in the separation tank 2 in the plating bath 10C, the bath temperature T3 of the adjustment tank 3 is 5 degreeC or more than the bath temperature T2 of the separation tank 2. It is preferable that it is high (T3≥T2 + 5 degreeC). Although bath temperature T1, T2, and T3 of each tank are controlled by an induction heating apparatus etc., the bath temperature fluctuation of about +/- 3 degreeC is usually inevitable from the limit of control precision. Considering such bath temperature control conditions, that is, the maximum value (target bath temperature + 3 ° C) and minimum value (target bath temperature -3 ° C) of bath temperature fluctuations, bath temperature T3 (target value) of the adjustment tank 3 is determined by the separation tank 2. It is preferable to make it at least 5 degreeC or more higher than bath temperature T2 (target value). Thereby, the Fe in the plating bath 10C of the adjustment tank 3 can be brought into a non-coated state. That is, the small diameter residual dross contained in the plating bath 10B transferred from the separation tank 2 can be reliably melt | dissolved and removed in the adjustment tank 3. When the temperature difference between bath temperature T3 and T2 is less than 5 degreeC, Fe unsaturation degree is inadequate and the residual dross which flowed in from the separation tank 2 into the adjustment tank 3 cannot fully be dissolved.

In addition, as long as the storage amount (capacity of the adjustment tank 3) Q3 [t] of the plating bath 10C in the adjustment tank 3 can carry out melt | dissolution, the holding | maintenance of bath temperature T3, and the bathing bath in the plating tank 1 as described above. Any amount may be sufficient and it is not specifically prescribed.

By the way, when the low Al concentration now (the said 2nd zinc containing now) is put into the adjustment tank 3, in the present surroundings immersed in the plating bath 10C of the adjustment tank 3, local bath temperature from the lowest to the current melting point. Since a drop occurs, dross is produced. In the plating bath 10 of the adjustment tank 3, since Fe is an unsaturated state, since the said produced dross dissolves relatively early, it is normally harmless. However, depending on the degree of Fe saturation of the adjustment tank 3 and the current dissolution time, the generated dross does not completely dissolve in the plating bath 10C, but may flow out to the plating bath 1.

Therefore, in this case, as in the fourth modified example shown in FIG. 8, the molten metal obtained by dissolving the present in the premelt tank 4 by providing a premelt tank 4 separately from the adjustment tank 3 is used. You may throw in the adjustment tank 3. Thereby, the molten metal preheated to the bath temperature T3 grade in the premelt tank 4 can be supplied to the adjustment tank 3, and the plating bath 10C of the adjustment tank 3 can prevent local temperature fall. . That is, the problem of dross generation accompanying the said injection | throwing-in in the adjustment tank 3 can be avoided.

In addition, during the hot-dip operation, a part of the plating bath 10B flows into the adjustment tank 3 through the communication tube 7 or the like from the separation tank 2 at the same time, and at the same time, the plating bath 10C in the adjustment tank 3. A part of the outflow to the plating tank 1 through the transfer pipe (8).

[3. Method for producing alloyed hot dip galvanized steel sheet]

Next, with reference to FIG. 10, the method (namely, the manufacturing method of an alloyed hot-dip galvanized steel plate) of the steel plate 11 is demonstrated using the above-mentioned hot-dip plating apparatus. FIG. 10 is a ternary state diagram showing the state transition of the plating bath 10 (GA bath) in each bath according to the present embodiment.

In the manufacturing method of the alloying hot-dip galvanized steel sheet which concerns on this embodiment, the plating bath 10 (GA bath) is made into the plating bath 1 (using the circulation part which has the said molten metal transfer apparatus 5, a flow path, etc.). For example, bath temperature: 460 degreeC, Al concentration: about 0.135 mass%, the separation tank 2 (for example, bath temperature: 440 degreeC, Al concentration: about 0.148 mass%), adjustment tank 3 (for example, , Bath temperature: 465 ° C, Al concentration: about 0.143 mass%). And in each tank of the plating tank 1, the separation tank 2, and the adjustment tank 3, the following processes are performed simultaneously simultaneously.

(1) Plating process in plating bath (1)

First, in the plating tank 1, the steel plate 11 immersed in this plating bath 10A is plated, maintaining 10A of plating baths stored in the plating tank 1 at predetermined | prescribed bath temperature T1. During this plating process, the plating bath 10C transferred from the adjustment tank 3 flows into the plating tank 1, and a part of plating bath 10A flows out from the plating tank 1 to the separation tank 2. As shown in FIG. In this plating bath 1, the steel plate 11 is always immersed in 10A of plating baths, Fe melt | dissolves from the said steel plate 11, and sufficient Fe supply is performed with respect to 10A of plating baths, so Fe The concentration is close to the saturation concentration. However, as described above, the time for the plating bath 10A to stay in the plating bath 1 is short (for example, 5 hours or less on average). Therefore, even if some operation fluctuations, such as a change in bath temperature, occur, no dross is produced until the Fe concentration of the plating bath 10A reaches the saturation point. It is only dross and does not grow to harmful dross of large diameter. In addition, the plating bath 1 is downsized than the conventional plating bath, and the time for which the circulating plating bath 10 stays in the plating bath 1 is shortened. Therefore, growth of dross to a nominal diameter in the plating tank 1 can be more reliably avoided.

(2) dross separation process in separation tank (2)

Subsequently, the circulation bath flowed out from the plating bath 1 is led to the separation bath 2. In the separation tank 2, Al in the plating bath 10B is maintained while the plating bath 10B stored in the separation tank 2 is maintained at a bath temperature T2 of 5 ° C or more lower than the bath temperature T1 of the plating tank 1. The concentration A2 is maintained at a high concentration of at least 0.14% by mass or more. In such a separation tank 2, Fe, which has become supersaturated in the plating bath 10B, is precipitated as a top dross, and a bottom dross of harmless diameter contained in the inflow bath from the plating bath 10 is used as the top draw. Transform into

For example, as shown in FIG. 10, when 10 A of plating baths of the said plating tank 1 are transferred to the separation tank 2, bath temperature T will rapidly change from T1 (460 degreeC) to T2 (440 degreeC). At the same time, the Al concentration rises from A1 (about 0.135 mass%) to A2 (about 0.148 mass%). As a result, in the plating bath 10B of the separation tank 2, Fe becomes a supersaturated state. Therefore, excessive Fe in the plating bath 10B of the separation tank 2 is crystallized as a top dross (Fe ₂ Al ₅ ). (晶 出) becomes. As described in Table 1, dross is easily generated when the bath temperature decreases. Also in the example of the GA bath in FIG. 10, the plating bath 10 transferred from the plating bath 1 to the separation tank 2 has a top draw according to the degree of supersaturation since Fe becomes supersaturated due to a decrease in bath temperature T. A large amount of gas is produced in the separation tank 2. At this time, Al concentration A2 of plating bath 10B is 0.14 mass% or more, for example, This is a high density | concentration which the state of plating bath 10B becomes a top dross | generating area | region under the conditions of bath temperature T2, Therefore, only top dross only Is generated, and little tom dross is generated. In this way, the top dross determined in the plating bath 10B of the separation tank 2 opens the inside of the plating bath 10B of the separation tank 2 by the specific gravity difference with the plating bath 10B (zinc bath). It floats and is separated and removed. In addition, since the Fe concentration of the plating bath 10B at the outlet of the separation tank 2 contains a small diameter residual dross not completely separated from the separation tank 2, the concentration is slightly higher than the Fe concentration saturation point. .

Since the capacity Q2 of the separation tank 2 is sufficiently large with respect to the bath circulation amount q, and the residence time of the plating bath in the separation tank 2 is 2 hours or more, most of the top dross is separated and floated out of the system. Removed. In addition, in order to maintain Al concentration A2 in the bath of this separation tank 2 at 0.14 mass% or more, for example, in order to maintain Al density | concentration Al higher than Al concentration A1 in the bath of the plating tank 1, The current (the first zinc-containing current) is added and dissolved in a small amount in the separation tank 2.

(3) Dross | melting melt | dissolution process in adjustment tank 3, and adjustment process of bath temperature and Al concentration

In addition, the circulation bath flowed out from the separation tank 2 is led to the adjustment tank (3). In the adjustment tank 3, while maintaining the bath temperature T3 of this adjustment tank 3 5 degreeC or more higher than the bath temperature T2 of the separation tank 2, Al concentration A3 of this adjustment tank 3 is Al of the plating tank 1 The concentration is higher than the concentration A1 and maintained at a concentration lower than the Al concentration A2 of the separation tank 2. In such adjustment tank 3, the dross contained in 10 C of plating baths is dissolved by making Fe in plating bath 10C into an unsaturated state. Thereby, the top diameter dross (residual dross) of the small diameter which could not be removed by the separation tank 2 can be melt | dissolved and removed in 10 C of unsaturated Fe states.

For example, as shown in FIG. 10, when the plating bath 10B from which the top dross was separated in the separation tank 2 is transferred to the adjustment tank 3, the bath temperature T is T3 (465 ° C) from T2 (440 ° C). This rapidly rises, and the Al concentration decreases from A2 (about 0.148 mass%) to A3 (about 0.143 mass%). As a result, in the plating bath 10C of the adjustment tank 3, since Fe becomes very unsaturated, the small diameter top dross (Fe ₂ Al ₅ ) remaining in the bath decomposes into Fe and Al relatively quickly. It dissolves and disappears. Thus, even when the residual dross is melt | dissolved, the plating bath 10C of the adjustment tank 3 is still Fe-saturated state.

In addition, the current (second zinc-containing current) for replenishing the molten metal consumed in the plating tank 1 is injected into and dissolved in the plating bath 10C of the adjustment tank 3. When the dross produced with the present melt | dissolution becomes a problem, as shown in FIG. 8, the premelt tank 4 is added to the adjustment tank 3, and it becomes the molten state in the premelt tank 4. What is necessary is just to supply it to the adjustment tank 3 now. In addition, the Al concentration of the circulation bath is made higher than necessary by injecting a high Al concentration current into the separation tank 2. For this reason, the replenishment now thrown into the adjustment tank 3 is made into the zinc containing now with low Al concentration, or the zinc containing now without Al. Due to such a low Al concentration, the Al concentration A3 in the bath of the adjustment tank 3 is lower than the Al concentration A2 in the bath of the separation tank 2, and the Al concentration A1 of the plating tank 1 is kept constant. To a suitable concentration.

After that, the plating bath 10C of the adjustment tank 3 which contains little dross and is also in an unsaturated state of Fe is led to the plating bath 1 and used in the plating process (1). While transferring the plating bath 10C from the adjustment tank 3 to the plating bath 1, the bath temperature T naturally decreases by the predetermined bath temperature drop width ΔT _fall . The plating bath 10C transferred from the adjustment tank 3 to the plating tank 1 contains almost no dross, and Fe is also in an unsaturated state. However, since Fe is eluted from the steel plate 11 immersed in the plating tank 1 in the plating bath 10A, Fe concentration in a bath gradually approaches around 0.03 mass% which is a saturation point in bath temperature T1 (460 degreeC). do. In addition, in the plating tank 1, the steel plate 11 and 10 A of plating baths react, and Al is consumed. Therefore, even if the plating bath 10C which has comparatively high Al concentration A3 (about 0.143 mass%) is transferred from the adjustment tank 3 to the plating tank 1, Al concentration A1 of the plating tank 1 will hardly rise. , It is adjusted to a substantially constant value (about 0.135 mass%).

As described above, the plating bath 1 is compact, and the residence time of the plating bath 10A in the plating bath 1 is short. Therefore, even if there is some operation fluctuation | variation, such as a bath temperature fluctuation, in the plating tank 1, until the Fe density | concentration in 10 A of plating baths reaches a saturation point (for example, 0.03 mass%), the plating tank 1 ), Neither Top Dross nor Bottom Dross are generated. Further, even if the Fe concentration in the bath in the plating bath 1 reaches the saturation point and a small diameter dross is produced, the dross is difficult to grow under the condition of constant bath temperature (see FIG. 2). Within a short residence time (eg, several hours) in), the resulting dross does not grow to a nominal diameter (eg, 50 μm or more). The small diameter dross produced in the plating bath 1 is transferred to the separation tank 2 and removed by floating separation before growing to a nominal diameter.

In addition, the Fe concentration of 10 A of plating baths of the said plating tank 1 changes with the capacity Q1 of the plating bath 1, the circulation amount q of a bath, the ease of dissolution of Fe, etc., for example. For this reason, although Fe in the plating bath 10A may be in an unsaturated state (when Fe concentration is less than 0.03 mass%), in this case, since Fe is unsaturated, dross is hard to produce | generate. On the contrary, although Fe in the plating bath 10A may be slightly supersaturated (when the Fe concentration is slightly larger than 0.03% by mass), even in this case, the dross generated in the plating bath 10A within a short time may be As it is a small diameter, it does not become a problem such as dross scratches.

As described above, the plating bath 10 is circulated in the order of the plating bath 1, the separation tank 2, and the adjustment tank 3, thereby inevitably occurring in the plating bath during the production of the alloy galvanized steel sheet. By removing the dross, it can be almost completely harmless. Therefore, the plating bath 10A of the plating tank 1 can maintain a dross free state at all times. Therefore, problems such as deterioration of the appearance of the steel plate surface due to dross adhesion, pressure scratches caused by the dross, roll slip due to precipitation of the dross onto the roll surface in the bath can be solved. When dross removal is performed using the manufacturing apparatus of this embodiment, it is not necessary to stop the plate of the plated steel sheet. In the plate of the plated steel sheet, the plating bath 10 is circulated in the order of the plating tank 1, the separation tank 2, and the adjustment tank 3. In other words, the dross is removed by continuous processing rather than batch processing. Therefore, the plating bath 10A of the plating bath 1 is always maintained in the clean state which is dross free.

Next, a method of adjusting the Al concentration in the plating bath 10 by inputting now is given to the plating bath 10 circulating between the tanks with reference to the state diagram of FIG. 10.

The Al concentration in the plating layer of the steel plate 11 is 0.3 mass% on average, for example, and is higher than Al concentration A1 (0.135 mass%) in 10 A of plating baths of the plating tank 1. That is, Al in the plating bath 10A is concentrated and plated on the plating layer of the steel plate 11. Therefore, when the current Al concentration supplied to the plating bath 10 is 0.135 mass%, the Al concentration of the plating bath 10A will gradually decrease. Therefore, in the conventional spot injection now, the Al concentration of 0.3-0.5 mass% was directly thrown into the plating bath, and Al concentration was hold | maintained.

In the hot-dip plating apparatus which concerns on this embodiment, it is a structure which transfers the plating bath 10 continuously from the adjustment tank 3 to the plating tank 1. In order to maintain Al density | concentration A1 of the plating tank 1 at 0.135 mass%, for example, the adjustment bath (3) of the plating bath 10 of which Al concentration is higher than 0.135 mass% (for example, 0.143 mass%) is carried out. It is necessary to continue supplying to the plating tank 1 from the following. Therefore, in order to maintain Al concentration A3 of the adjustment tank 3 at about 0.143 mass% of the target, Al is actively supplied to the separation tank 2, and Al concentration A2 of the separation tank 2 is higher than A3 (for example, For example, 0.148 mass%). Further, in the separation tank 2, it is preferable to set the Al concentration A2 in the bath of the separation tank 2 to a high concentration in order to deposit and remove as many top dross as possible. Therefore, as a 1st zinc containing now, the present containing a high concentration of Al (for example, 10 mass% Al-90 mass% Zn) is thrown into the separation tank 2, and the plating bath of the separation tank 2 ( Increase Al concentration A2 of 10B). Here, the amount of Al introduced into the separation tank 2 is equal to the sum of the amount of Al consumed as the top dross in the separation tank 2 and the amount of Al consumed in the plating layer of the steel sheet 11 in the plating tank 1. It is considerable.

On the other hand, in the adjustment tank 3, as a 2nd zinc containing now, the content rate of Al is low and the content rate of Zn is high (for example, zinc containing 0.1 mass% Al-Zn now or zinc which does not contain Al). Now containing). As a result, the Al concentration of the plating bath 10B transferred from the separation tank 2 to the adjustment tank 3 is decreased, and the Al concentration A3 in the plating bath 10C of the adjustment tank 3 is determined by the separation tank 2. It adjusts before and after Al density | concentration (for example, 0.143 mass%) in the middle of Al concentration A2 and Al concentration A1 of the plating tank 1. Then, by transferring the plating bath 10C from the adjustment tank 3 to the plating bath 1, the Al concentration A1 in the bath of the plating bath 1 is adjusted to an appropriate concentration (for example, 0.135 mass%) for producing GA. ) Can be maintained.

Thus, in the hot-dip plating apparatus which concerns on this embodiment, it puts into a separation tank 2 and the adjustment tank 3, and spreads a plating bath and adjusts components of a plating bath, for example, Al concentration. Therefore, since it is not necessary to inject | pour right now directly into the plating tank 1, dross generation | occurrence | production accompanying a bath temperature change of the surroundings can be prevented now.

[4. Technical significance of installing separation tank and adjusting tank]

Next, in the plating apparatus according to the present embodiment, in addition to the plating tank 1, two tanks, namely, the separation tank 2 and the adjustment tank 3, are additionally installed, and not only the bath temperature T of the circulation bath, but also the circulation bath. The technical significance of controlling Al concentration is also explained in full detail.

As described above, in the present embodiment, by increasing the Al concentration A2 in the bath in the separation tank 2, the adjustment concentration of the Al concentration A3 in the bath is adjusted in the bath 3 while promoting precipitation and separation of the top dross in the bath. By lowering, the Al concentration of the plating bath returned to the plating bath 1 is adjusted to an appropriate concentration. Thus, even if GA is manufactured using GA bath (Al concentration: 0.125-0.14 mass%) whose Al concentration is lower in bath compared with GI bath by controlling Al concentration of a circulation bath appropriately, 1 It is possible to raise the Al concentration A3 of the separation tank 2 to the high concentration (for example, 0.147 mass% or more) required for depositing the top dross while maintaining the Al concentration A1 in the bath of the bath) at a desired low concentration. . Therefore, in the separation tank 2, only the top dross can be precipitated without depositing the bottom dross, and the said top dross can be floated suitably. That is, since the bottom dross is not included in the circulation bath, it is possible to prevent the bottom dross from being refluxed into the plating bath 1 to be a cause of dross scratches. Below, this principle is explained in full detail.

[4.1. Condition of Al Concentration A2 in Bath of Separation Tank 2]

First, with reference to FIG. 11, the conditions (especially the conditions of Al concentration A2 in the bath of the separation tank 2) for making dross precipitated in the separation tank 2 into a top dross are demonstrated. 11 is a ternary system state diagram for explaining a state of the GA bath according to the present embodiment.

As shown in FIG. 11, the state (bath temperature and composition) of the plating bath is a bottom dross generation region, a bottom dross / top dross hybrid region (hereinafter referred to as a "hybrid region"), and a top dross generation region. Are distinguished. If the Fe concentration in the plating bath and the bath temperature T are constant, as the Al concentration in the bath becomes high, the state of the plating bath moves in the order of the bottom dross generation region, the hybrid region, and the top dross generation region.

Here, the state of the plating bath 10A (GA bath) of the plating tank 1 is the state S1 (bath temperature T1: 460 degreeC, Fe concentration: 0.03 mass%, Al concentration A1: 0.13 mass%) shown in FIG. Think of the case. In this case, when the plating bath 10A of the said state S1 is transferred to the separation tank 2, the Al concentration A2 in the bath of the separation tank 2 is raised, and the bath temperature T2 is lowered, A dross containing dross precipitates. However, if Al concentration A2 in the bath of the separation tank 2 is not made high enough, since a bath state will be a hybrid region, top dross and a bottom dross will hybridize. On the other hand, when Al concentration A2 in the bath of the separation tank 2 is made high enough so that a bath state may become a top dross production | generation area | region, only a top dross is produced | generated and a bottom dross is hardly produced | generated.

Since the Al concentration A2 in the bath of the separation tank 2 is insufficient, when the bottom dross and the top dross are mixed, the top dross can be relatively easily removed and removed. However, the bottom dross has a small specific gravity difference with respect to the molten metal, and cannot be separated efficiently. For this reason, since the bottom dross floats in the bath of the separation tank 2 through the bath in the separation tank 2, the Fe concentration of the separation tank 2 is not reduced. In addition, the bottom dross generated in the separation tank 2 may be refluxed to the adjustment tank 3 and further to the plating tank 1 through the bath. Therefore, in view of efficiently separating the dross, in the separation tank 2, the Al concentration A2 in the bath is raised to a sufficiently high concentration, so that all of the precipitated dross is made into the top dross and the bottom dross is not produced. It is preferable.

Therefore, in order to obtain the conditions that all the dross precipitated in the separation tank 2 turns into a top dross, it examined using the state diagram shown in FIG. 11, and the following conclusion was obtained.

For example, as shown to S1 to S5 of FIG. 11, GA bath of the plating tank 1 is called state S1 (Al concentration A1: 0.13 mass% in bath, bath temperature T1: 460 degreeC). When the GA bath is transferred to the separation tank 2 of the bath temperature T2, the condition that the bath state becomes the top dross generating region is (1) when the bath temperature T2 of the separation tank 2 is 450 ° C, When Al concentration A2 is 0.147 mass% or more in the bath of tank (2) (state S3), and (2) when bath temperature T2 is 440 degreeC, it is necessary for Al concentration A2 in a bath to be 0.154 mass% or more (state S5). .

In addition, as shown in S6-S9 of FIG. 11, GA bath of the plating tank 1 is called state S6 (Al concentration A1: 0.14 mass% in bath, T1: 460 degreeC in bath temperature). Similarly, the condition under which the plating bath state becomes the top dross generating region is (1) when the bath temperature T2 of the separation tank 2 is 450 ° C, the Al concentration A2 in the bath of the separation tank 2 is 0.143 mass% or more. (State S7) and (2) When bath temperature T2 is 440 degreeC, it is necessary for Al concentration A2 in a bath to be about 0.15 mass% or more (state S9).

FIG. 12 is a graph summarizing the conditions of Al concentration A2 in the bath of the separation tank 2 and shows bath conditions in which all the precipitation drosses can be the top dross in the separation tank 2. The boundary lines L1 and L2 in FIG. 12 represent the lower limit values of the Al concentration A2 in the bath for making all the precipitation drosses as the top dross according to the bath temperature T2 of the separation tank 2, and L1 represents the Al concentration A1 in the baths of the GA bath. In the case of 0.13, L2 is a boundary when Al concentration A1 is 0.14 mass% in the GA bath.

As shown in FIG. 12, when Al concentration A1 in the bath of the plating tank 1 is 0.13 mass%, the bath state (bath temperature T2, Al concentration A2) of the separation tank 2 is S2, S3, S4, and S5. In the case of belonging to the region on the upper right side of the line segment L1 connecting four points of, the Al concentration A2 in the bath is higher than the lower limit, and the bath state becomes the top dross generating region. Precipitates. Moreover, when Al concentration A1 is 0.14 mass% in the bath of the plating tank 1, even when the bath state of the separation tank 2 belongs to the area | region of the upper right side rather than the line segment L2 which connects three points of S7, S8, and S9. Similarly, since the bath state becomes the top dross generating region, only the top dross is precipitated in the separation tank 2.

As mentioned above, the conditions of Al concentration A2 in the bath for making all the precipitation dross top saw in the separation tank 2 are the state (Al concentration A1, Fe concentration) of the GA bath of the plating tank 1, and the separation tank. It is determined by the bath temperature T2 of (2). Therefore, the bath state of the separation tank 2 is raised by raising Al concentration A2 in the bath of the separation tank 2 to a high concentration according to the bath state of the plating tank 1 and the bath temperature T2 of the separation tank 2. It is possible to shift from the dross generating region or the hybrid region to the top dross generating region and to deposit only the top dross in the separation tank 2.

[4.2. Necessity of Coordination Group]

As described above, the higher Al concentration A2 in the bath of the separation tank 2 contributes to the precipitation of only the top dross in the separation tank 2. However, if the Al concentration A2 in the bath of the separation tank 2 is excessively high, the plating bath of high Al concentration will be refluxed to the plating tank 1. If the circulation of the plating bath is continued, the Al concentration A1 in the bath of the plating bath 1 gradually increases to deviate from the desired concentration suitable for the GA bath. Therefore, in this embodiment, the adjustment tank 3 is provided between the separation tank 2 and the plating tank 1, and the plating bath of the high Al concentration A2 conveyed from the separation tank 2 in the said adjustment tank 3 is carried out. 10B is thinned to an appropriate Al concentration, and then transferred to the plating bath 1. By the function of the adjustment tank 3, while maintaining the Al concentration A1 in the bath of the plating tank 1 at a constant concentration suitable for the GA bath, while raising the Al concentration A2 in the bath of the separation tank 2 to the high concentration. It becomes possible.

By the way, since this embodiment aims at GA bath | substrate which is lower in Al concentration in a bath compared with GI bath, the necessity of installing the adjustment tank 3 which readjusts Al concentration of a plating bath becomes high. This reason is demonstrated below.

Unlike the present embodiment, when producing GI using the GI bath, since the Al concentration A1 in the bath of the plating bath 1 is 0.15 to 0.25 mass%, the Al concentration of the circulating bath and the separation bath 2 Al concentration A2 in a bath also necessarily becomes at least 0.15 mass% or more. Therefore, the bath state of the GI bath in the separation tank 2 always becomes the top dross generating region (see FIG. 1). In the separation tank 2, when a normal zinc dust is put in, the top dross is precipitated only by lowering the bath temperature T2 than the bath temperature T1, and the floating surface can be separated from the bath surface. Therefore, in the case of a GI bath, it is not necessary to necessarily provide the adjustment tank 3 for readjusting bath composition.

On the other hand, when manufacturing GA using GA bath by the method which concerns on this embodiment, in order to ensure the alloying speed in the plating layer of the steel plate 11, Al concentration A1 in the bath of the plating tank 1 is carried out. It is necessary to make relatively low concentration of 0.125-0.14 mass%. For this reason, if Al concentration A2 in a bath is not made high enough, the bath state of GA bath in the separation tank 2 may become a bottom dross production | generation area or a mixed area, and there exists a danger that a bottom dross may precipitate. .

Therefore, in the case of the GA bath, in order to precipitate only the top dross in the separation tank 2, it is necessary to increase the Al concentration A2 in the bath of the separation tank 2 to the target concentration. For example, as shown in FIG.11 and FIG.12, when Al concentration is 0.13 mass% in the GA bath | bath, and bath temperature T2 is reduced to 450 degreeC in the separation tank 2, and a dross is precipitated, it isolate | separates. If the Al concentration A2 in the bath of (2) is not 0.147 mass% or more, it is not possible to deposit only the top dross without depositing the bottom dross (condition 1).

However, when Al concentration A2 in the bath of the separation tank 2 is made high too much, Al amount in the plating bath which flows back from the separation tank 2 to the plating tank 1 will greatly reduce the Al consumption in the plating tank 1. It will exceed. Therefore, Al concentration A1 in the bath of the plating tank 1 rises and it deviates from a suitable density | concentration. Therefore, in order to maintain Al concentration A1 in the bath of the plating tank 1 at a constant concentration suitable for the GA bath, considering the bath circulation amount q, the Al concentration A2 in the bath transferred from the separation tank 2 is somewhat low. Must be suppressed (condition 2).

Therefore, in order to satisfy both of these two opposing conditions 1 and 2, the inventor of the present invention calculates the Al concentration A2 in the bath of the separation tank 2 that can be achieved under operating conditions of general alloyed hot dip galvanizing. In this regard, appropriate operating conditions were reviewed. As a result, when operating only in the separation tank 2 without providing the adjustment tank 3, it turned out that neither of said conditions 1 and 2 can be satisfied, and wide GA operation cannot be performed.

For example, in the following operating conditions A, when the adjustment tank 3 is not provided, Al concentration A2 in the bath of the separation tank 2 is made into 10 degree / h by the restriction | limiting of the said condition 2, and bath circulation amount q is 10 t / h. Can be increased to 0.145% by mass and only 0.140% by mass when the bath circulation amount q is 15 t / h. For this reason, since Al concentration A2 in the bath of the separation tank 2 will be less than 0.147 mass% of the lower limit required for depositing only the top dross mentioned above, bottom dross is produced | generated in the separation tank 2. Moreover, when bath circulation amount q is extremely small at 6 t / h, Al concentration A2 in the bath of the separation tank 2 will be 0.155 mass%, and becomes higher than the said lower limit of 0.147 mass%. However, since the bath circulation amount q is too small, it takes time for the plating bath 10A of the plating bath 1 to be replaced, for example, when the capacity of the plating bath 1 is 40t, on average, 6.6 hours Needs replacement time. For this reason, there exists a problem that bottom dross generate | occur | produces in 10 A of plating baths which stayed in the plating tank 1.

<Operation condition A>

Metal consumption in the plating bath 1: 900kg / ㎡

Plate width of steel plate 11: 900 mm

Plating Speed: 150m / min

Bath temperature T1 of the plating bath (1): 460 degreeC

Bath temperature T2 of the separation tank 2: 450 degreeC

Al concentration A1: 0.130 mass% in the bath of the plating tank 1

Bath circulation q: 6t / h, 10t / h, 15t / h

In addition, in the following operating conditions B, when the adjustment tank 3 is not provided, even when bath circulation quantity q is any of 6t / h, 8t / h, 10t / h, 15t / h, by the restriction | limiting of the said condition 2 The Al concentration A2 in the bath of the separation tank 2 can be raised only to 0.136 to 0.144 mass%. Since Al concentration A2 in the bath of the separation tank 2 will be less than 0.147 mass% of the lower limit required in order to precipitate only the top dross mentioned above, a bottom dross will produce | generate in the separation tank 2.

<Operation condition B>

Metal consumption in the plating bath 1: 500kg / ㎡

Plate width of steel plate 11: 700 mm

Plating Speed: 120m / min

Bath temperature T1 of the plating bath (1): 460 degreeC

Bath temperature T2 of the separation tank 2: 450 degreeC

Al concentration A1: 0.130 mass% in the bath of the plating tank 1

Bath circulation q: 6t / h, 8t / h, 10t / h, 15t / h

As described above, in the case of using a GA bath having a lower Al concentration than the GI bath, if the adjustment tank 3 is not provided, the Al concentration A2 in the bath of the separation tank 2 is sufficiently limited by the condition 2 above. It cannot be made high and said condition 1 cannot be satisfied. For this reason, the method which does not provide the adjustment tank 3 has a big problem in the response force to wide GA operating conditions, and cannot apply to operation of GA bath.

On the other hand, according to the method of providing the adjustment tank 3 which concerns on this embodiment, the adjustment tank 3 can finally adjust Al density | concentration A3 in the bath of the plating bath highly concentrated in the separation tank 2. As shown in FIG. For example, it becomes possible to reduce Al concentration A2 in the bath which rose too much in the separation tank 2 to Al concentration A3 in the low bath suitable for returning to the plating tank 1.

For example, in the above-mentioned operating condition A, when (1) bath circulation quantity q is 6t / h, when Al concentration A2 of the separation tank 2 is 0.182 mass%, and (2) bath circulation quantity q is 10t / h When Al concentration A2 of the separation tank 2 is 0.159 mass%, and (3) bath circulation quantity q is 15 t / h, Al concentration A2 of the separation tank 2 can be raised to 0.149 mass%. Thus, Al concentration A2 of the separation tank 2 can be made into a density | concentration sufficiently higher than 0.147 mass% which is a lower limit of the said condition 1. In addition, in the above-mentioned operating condition B, when the bath circulation amount q is 6t / h, the Al concentration A2 of the separation tank 2 is up to 0.157 mass%, and when the bath circulation amount q is 8t / h, the Al concentration of the separation tank 2 is used. A2 can be raised to 0.150 mass%. Thus, Al concentration A2 of the separation tank 2 can be made into a density | concentration sufficiently higher than 0.147 mass% which is a lower limit of the said condition 1.

As mentioned above, by providing the adjustment tank 3 which concerns on this embodiment, the 2nd zinc containing wedge (low Al concentration now or zinc free which does not contain Al) is thrown into the adjustment tank 3, and a plating bath (10C) Al concentration of A) can be lowered. Thereby, it is possible to make Al concentration A2 high enough in the bath of the separation tank 2 by putting high Al concentration now into the separation tank 2. For example, even if Al concentration A2 in the bath of the separation tank 2 is raised to a high concentration (for example, 0.159 mass%), the concentration of the plating bath 10C is readjusted in the adjustment tank 3, and Al in the bath is adjusted. The density | concentration A3 can be reduced to low density | concentration (for example, 0.145 mass%). As a result, when 10 C of plating baths of the adjustment tank 3 are returned to the plating tank 1, Al concentration A1 in the bath of the plating tank 1 will be continuously made to the desired constant density (for example, 0.13 mass%). I can keep it.

As described above, when the adjusting tank 3 is provided, the top dross precipitation and floating separation effect in the separating tank 2 can be exhibited under almost all GA operating conditions as described above. Further, by setting the bath temperature T3 of the adjustment tank 3 to be higher than the bath temperature T2 of the separation tank 2, the Fe melting limit in the plating bath 10C is increased, the Fe unsaturation is secured, and thus the residual dross Dissolution promotion is more effectively performed, and there is a composite effect that dross-free can be stably achieved.

[4.3. Control of Bath Circulation Rate by Increasing / Decreasing Al Concentration in Plating Baths]

As described above, the operating conditions satisfying both of the condition 1 and the condition 2 are changed by the Al concentration A1 and the bath circulation amount q in the bath of the plating bath 1. Therefore, by controlling the bath circulation amount q according to the increase or decrease of the Al concentration A1 in the bath of the plating tank 1, the Al concentration A2 in the bath of the separation tank 2 can be maintained to a desired high concentration, and the conditions 1 and 2 It becomes possible to satisfy both.

That is, since Al consumption amount per unit time by the plating process in the plating tank 1 is constant, when there is much bath circulation amount q, there exists a restriction that Al concentration A2 in the bath of the separation tank 2 cannot be made high. Therefore, when operating by changing operating conditions from the high bath state to the low bath state in Al bath A1 in the bath in the plating tank 1 (for example, when the Al concentration is 0.125-0.13 mass%, In the case of producing GA in the GA bath, the bath circulation amount q of the GA bath may be reduced. Thereby, since the quantity of GA bath returned from the adjustment tank 3 to the plating tank 1 per unit time decreases, Al concentration of the GA bath can be made higher than before the operation change. Therefore, the Al concentration A2 in the bath of the separation tank 2 can be maintained at a high concentration, and it is possible to maintain the bath state of the separation tank 2 as the top dross generating region.

For example, when producing high tensile strength steel, an additive element such as silicon or manganese is added to the steel in order to increase the strength. However, when the additive element is added in a large amount, it is known that the alloying rate of GA is significantly lowered. In order to overcome this, Al concentration A1 in the bath of the plating tank 1 may be reduced. For example, when Al concentration A1 is operated at 0.14 mass% in the bath of the plating tank 1, it can be made easy to alloy in the plating layer of the steel plate 11 by reducing A1 to 0.13 mass%.

As described above, when the Al concentration A1 in the bath of the plating bath 1 is reduced by changing the operating conditions, the amount of bath circulation q may be reduced than before the change in order to deposit only the top dross in the separation bath 2. Since the amount of Al supplied to the plating tank 1 per unit time is reduced by such a decrease in the bath circulation amount q, it is possible to maintain a balance between the consumption amount of Al in the plating tank 1 and the supply amount. Therefore, even if Al concentration A2 in the bath of the separation tank 2 is maintained at a high density | concentration more than the lower limit of the said condition 1, since Al concentration A1 in the bath of the plating tank 1 does not rise, both of the said conditions 1 and 2 are Can satisfy. Therefore, while performing plating process using the GA bath of the composition after the change in the plating tank 1, only the top dross is precipitated in the separation tank 2, and it becomes possible to isolate | separate.

On the other hand, when the Al concentration A1 in the bath of the plating bath 1 is increased by changing the operating conditions, the bath circulation amount q may be increased to an amount suitable for the Al concentration A1 in the bath after the increase. Thereby, since the balance of the consumption amount of Al and the replenishment amount in the plating tank 1 can be maintained, both of the said conditions 1 and 2 can be satisfied.

In addition, it is possible to control the bath circulation amount q by the molten metal transfer device 5 of the circulation section adjusting the bath delivery amount per unit time. What is necessary is just to calculate | require the bath circulation amount q suitable for Al concentration A1 in the bath of the plating tank 1 by prior experiment or calculation.

[4.4. theorem]

The above-mentioned examination analyzes the ternary state of iron-zinc-aluminum and its temperature dependence, considers the actual GA operating conditions and the situation of dross scratches, their causes, and further, the generation, growth, The details of the disappearance can be clearly understood. Therefore, in order to obtain the plating bath in which no harmful dross exists, the technique which combines the conditions of the separation tank 2 (bath temperature T2, Al concentration A2) and the conditions of the adjustment tank 3 (adjustment of bath temperature T3, Al concentration A3) Is hardly found only from the well-known techniques described in Patent Documents 1 to 5.

In the above, the manufacturing apparatus and method of the alloying hot dip galvanized steel plate which concerns on this embodiment were demonstrated in detail. According to this embodiment, the dross which inevitably arises at the time of manufacture of a zinc-aluminum type hot-dip steel plate can be removed efficiently and effectively by the separation tank 2 and the adjustment tank 3, and can be almost completely harmless. As a result, in order to avoid curling of the dross in the plating bath 10, the phenomenon of sacrificing productivity by suppressing the plate speed (plating speed) of the steel sheet 11 can be improved, and the plating speed can be increased. The productivity improvement of an alloying hot dip galvanized steel plate is aimed at.

Example 1

[5. [Example]

Next, an embodiment of the present invention will be described. In addition, the following example shows the test done to verify the effect of this invention to the last, and this invention is not limited to the following example.

[5.1. Test 1: Plating test of alloyed hot dip galvanized steel sheet (GA)]

A cyclic plating apparatus (corresponding to the hot dip plating apparatus according to the above embodiment) was installed in a pilot line, and a continuous plating test for producing an alloyed hot dip galvanized steel sheet (GA) was performed. In Table 2, the conditions of the said continuous plating test are shown. In addition, as a comparative example, the same test was done also about the conventional plating apparatus provided only with a plating tank. Here, in Table 2 _-2 ΔT ₁ shows a plating tank 1 yokon T1 and separation tank 2 yokon difference (= T1-T2) of the yokon T2.

(1) conventional plating apparatus

Plating tank capacity Q1: 60t

(2) circulating plating equipment

Plating tank capacity Q1: 10t, 20t, 40t

Separator capacity Q2: 40t, 12t

Adjusting tank capacity Q3: 20t

Circulation amount of bath q: 10t / h, 6t / h

Using this plating apparatus, the coil of plate | board thickness 0.6mm x plate | board width 1000mm was plated continuously for 12 hours at the target plating weight of 100 g / m <2> (both sides), and a plating speed of 100 m / min. Bath temperature drop width (DELTA) T _fall at the time of the bathing from the adjustment tank 3 to the plating tank 1 was 2-3 degreeC.

At the beginning of plating and at the end of plating, samples of the baths are quenched and samples are taken. The type of dross included in the bath and the diameter and number of dross per fixed observation area are examined to determine the dross weight per unit volume (dross density). Was obtained. After completion of the experiment, the bath of the plating bath 1 was discharged and the presence or absence of sediment dross at the bottom of the bath was observed.

In addition, the Al concentration and the Fe concentration of each bath were measured every 4 hours.

At the time of plating start, since each group was Fe-saturated state, dross was hardly present.

All the tanks were ceramic pots, and induction heating was used as a heating device of each tank thermal insulation section. The bath temperature control precision of each heat insulation part was within +/- 3 degreeC. Moreover, the circulation part of the circulation type plating apparatus overflows the transfer of the plating bath from the adjustment tank 3 to the plating tank 1, and the transfer of the plating bath from the plating tank 1 to the separation tank 2 overflows. The transfer of the plating bath from the separation tank 2 to the adjustment tank 3 was configured to use the communication pipe 7.

In order to control Al density | concentration in the bath of the separation tank 2 and the adjustment tank 3, 10 mass% Al-Zn now was injected into the separation tank 2 at substantially equal intervals. In the adjustment tank 3, the now 100 mass% Zn was injected as needed, visually monitoring so that a bath surface level might become substantially constant. On the other hand, in the case of the conventional plating apparatus, the combination current was directly put into the plating tank.

The test results are shown in Tables 3 and 4. Table 3 shows the Al concentrations and the Fe concentrations of the plating bath, the separation tank, and the adjustment tank at the time of 12 hours of operation, and Table 4 shows the density of the floating dross and the settling bottom of the plating tank in the plating tank at the time of 12 hours of operation. The visually confirmed amount of loss is shown.

In addition, the target value of the dross density is quantitatively verified by analyzing the plating bath obtained under the operating conditions in which the dross is not a problem at all because the sheet speed of the steel plate 11 is relatively low among the operating conditions for the developing GA. It was. This obtained "0.15 mg / cm <3> or less" as a target value of a top dross density, and "0.60 mg / cm <3> or less" as a target value of a bottom dross density.

According to the said test result, as shown in Table 3 and Table 4, in Examples 1-7, the dross density was below the target value and the dross removal effect was confirmed. In particular, in Examples 1 and 2, dross was almost eliminated, and roughly dross free was achieved. In addition, in Example 3, generation and growth of bottom dross in the plating bath 1 were observed. This is because, in Example 3, the capacity Q1 of the plating bath 1 is about 6.7 times (= 40/6) of the bath circulation amount q per hour, which is larger than 5 times as a reference, and therefore, such a large plating bath 1 It is considered that the residence time of the plating bath in the interior is long, and dross is produced and grown in the bath of the plating bath 1. In Example 4, it was confirmed that the top dross was refluxed in the plating bath 1. The reason for this is that in Example 4, since the capacity Q2 of the separation tank 2 is 1.2 times (= 12/10) of the bath circulation amount q per hour, and is less than 2 times as a reference, the separation tank 2 is rarely used. It is presumed that it is not possible to secure sufficient time to separate the loss from the loss, and the dross separation effect is inferior.

On the other hand, in the comparative example 1, although the large dross did not exist, there existed many small diameter and medium diameter bottom dross and top dross. This is considered to be because the bath temperature T2 of the separation tank 2 was made the same as the bath temperature T1 of the plating tank 1, and the dross removal effect in the separation tank 2 was reduced. Moreover, in the comparative example 2 of the conventional plating bath, in addition to the small diameter and the medium diameter bottom dross, a large bottom dross was also observed and the density of the top dross was also high. This is considered to be because both the bottom dross and the top dross were precipitated by the operation fluctuation because the Al concentration of the plating bath was close to the branching point between the top dross generating region and the bottom dross generating region.

In addition, as shown in Table 2, bath temperature T1 of the plating tank 1 is set to 454 degreeC in Example 5, 455 degreeC in Example 6, and 456 degreeC in Example 7 as bath temperature T2 of the separation tank 2 is carried out. (460 ℃) and a _{1 -2} yokon difference ΔT (= T1-T2) of yokon T2 of the separation tank 2, example 5, 6 ℃, example 6, conducted ℃ 5, example 7, set to 4 ℃ It was. From Examples 5 to 7, the effect of the bath temperature difference ΔT _{1 -2} on the dross production was verified. Since the result, as shown in Table 4, Examples 1 to 6 For, yokon T2 of yokon difference ΔT _{1 -2} of yokon T1 and separating tank (2) of the bath (1) is more than 5 ℃ (T1- T2 ≧ 5 ° C.) and the suspended dross density is remarkably small, and the effects of the present invention are sufficiently obtained. Thus, while for Example yokon difference ΔT _{1 -2} 7, such as the case of less than 5 ℃ If the next (for example, 4 ℃) (T1-T2 <5 ℃), the floating dross density approaches the target upper limit value A small amount of sedimentation dross was also generated, and the effect of the present invention was obtained, but it was found that the level was lowered. Thus, yokon T2 of yokon difference ΔT _{1 -2} of the separation tank 2 for yokon T1 of the plating vessel (1) can be said to be preferably not less than, 5 ℃.

5.2. Test 2: Verification Test of Separation Efficiency of Bottom Dross and Top Dross]

Next, test results performed to verify the separation efficiency of the bottom dross and the top dross using specific gravity separation will be described.

The specific gravity of the top dross is 3900 to 4200 kg / m 3, and the specific gravity of the bottom dross is 7000 to 7200 kg / m 3.

In the separation tank 2 having a width of 2.8 m x length 3.5 m x height 1.8 m (capacity 120 t), dross flotation (sedimentation) separation in the case of a bath circulation amount of 40 t / h was analyzed by flow simulation. The result of was obtained. Table 5 shows the specific gravity separation efficiency of the top dross and the bottom dross.

According to the said test result, as shown in Table 5, in all cases of particle size 50 micrometers, 30 micrometers, and 10 micrometers, the separation efficiency of the top dross was higher than the bottom dross. Therefore, it can be seen that it is effective to perform specific gravity separation of the dross in the state of the top dross.

[5.3. Test 3: Verification Test of Separator Capacity]

Next, the test result which examined the capacity | capacitance Q2 of the separation tank 2 which is necessary for floating separation of the top dross in the separation tank 2 using flow analysis is demonstrated. The preconditions of this analysis are as follows.

Bath circulation amount: 40t / h

Separator tank capacity: 20 to 160t

Top dross diameter: 30㎛

The result of the said analysis test is shown in FIG. As shown in FIG. 13, when the capacity | capacitance Q2 of the separation tank 2 becomes 2 times or more of the plating bath circulation quantity q (40 t / h) per hour, dross | separation ratio becomes 80% or more. When the capacity | capacitance Q2 of the separation tank 2 becomes less than 2 times of the bath circulation quantity q, the dross | separation separation ratio falls rapidly. From these results, it was found that the capacity Q2 of the separation tank 2 is preferably at least two times the amount of the bath circulation q [(Q2 / q)? 2].

[5.4. Trial 4: Verification Test of Plating Tank Capacity]

Next, in order to confirm the residence time of the plating bath 10A in which the dross generated in the plating bath 10A (GA bath) of the plating bath 1 does not grow up to the nominal diameter, a pilot line of alloyed hot dip galvanizing is performed. The results of the bath cycle test will be described. This test condition is as follows.

Plating bath standard bath temperature T1 (target bath temperature): 460 ° C

Al concentration in bath: 0.136 mass%

Fe concentration in bath: Saturated (0.03% by mass)

Steel plate: Plate thickness 0.6 mm × plate width 1000 mm

Plating Speed: 100m / min

Plating adhesion amount: 100g / ㎡ (both sides)

Bath temperature fluctuation: ± 5 degrees Celsius (we changed intentionally by controlling heater output)

Plating tank capacity Q1: 60t

Bath circulation q: 5 to 60 t / h

After changing the bath circulation amount, the bath circulation amount q until the plating bath in the plating tank 1 was completely replaced was made constant. Specifically, the bath circulation was continued until circulation plating three times the capacity Q1 of the plating tank 1 was completed.

Immediately before the one-level bath circulation test was completed, a sample was taken from the plating bath overflowing from the plating bath 1, and the diameter of the dross present in the bath was measured.

In addition, in actual operation, the bath temperature variation of the plating bath 1 is usually smaller than ± 5 ° C, which is the current test condition, and is about ± 3 ° C. However, in order to confirm the conditions under which dross detoxification can be stably achieved, a test was conducted under conditions in which dross generation and growth were more likely to occur than usual.

The results of the test are shown in FIG. As shown in FIG. 14, when the bath circulation amount q per hour is less than 12 t / h (that is, when the capacity Q1 of the plating tank 1 exceeds 5 times the bath circulation amount q per hour: (Q1 / q)> 5 ] The maximum diameter of the dross actually observed was larger than the nominal diameter (50 micrometers). The reason for this is considered to be that the dross has remarkably grown until the diameter of the plating bath becomes long because the plating bath stays in the plating bath 1 for a long time. On the other hand, when the bath circulation amount q per hour is 12 t / h or more (that is, when the capacity Q1 of the plating tank 1 is 5 times or less than the bath circulation amount q per hour: (Q1 / q) ≤ 5), the nominal diameter (50 Only small diameter dross (about 27 micrometers or less) sufficiently smaller than the micrometer) was observed. This is considered to be because the residence time in the plating bath 1 of the plating bath is short and dross does not sufficiently grow. Therefore, it turned out that it is preferable that the capacity | capacitance Q1 of the plating tank 1 is 5 times or less of the bath circulation quantity q per hour.

[5.5. Test 5: Verification Test of Proper Range of Plating Bath Inflow Bath Temperature]

Next, the result of having performed the test which verifies about the appropriate range of bath temperature T3 of the plating bath 10C which flows into the plating tank 1 from the adjustment tank 3 is demonstrated. When the bath temperature T3 of the plating bath 10C flowing into the plating bath 1 from the adjustment tank 3 is largely shifted from the bath temperature T1 of the plating bath 1, the bath temperature variation in the plating bath 1 is promoted, and as a result, plating is performed. It is expected to promote dross production and growth in the tank (1). For this reason, the confirmation test of the appropriate range of bath temperature T3 of the adjustment tank 3 was performed using the pilot line of alloying hot dip galvanizing. The test conditions are as follows.

Plating bath standard bath temperature T1 (target bath temperature): 460 ° C

Al concentration in bath: 0.136 mass%

Fe concentration in bath: Saturated (0.03% by mass)

Steel plate: Plate thickness 0.6 mm × plate width 1000 mm

Plating Speed: 100m / min

Plating adhesion amount: 100g / ㎡ (both sides)

Bath temperature fluctuation: ± 5 degrees Celsius (we changed intentionally by controlling heater output)

Plating tank capacity Q1: 60t

Bath circulation q: 20t / h

Inflow bath temperature (T3-ΔT _fall ): 445 to 480 ° C. [ΔT _fall is a bath temperature drop width, which is a bath temperature that naturally drops during the transfer of the plating bath from the adjustment tank 3 to the plating bath 1]

After changing the inflow bath temperature, the bath circulation amount q until the plating bath in the plating bath 1 was completely replaced was made constant. Specifically, the circulation of the bath was continued until the plating bath three times the capacity Q1 of the plating tank 1 was completed.

Immediately before completion of the one-level bath circulation experiment, a sample was taken from the plating bath overflowing from the plating bath, and the diameter of the dross present in the bath was measured.

In addition, in actual operation, the bath temperature variation of the plating bath 1 is usually smaller than ± 5 ° C, which is the present experimental condition, and is about ± 3 ° C. However, in order to confirm the conditions under which dross detoxification can be stably achieved, experiments were conducted under conditions in which dross generation and growth were more likely to occur than usual.

The results of the test are shown in FIG. 15. As it is shown in Figure 15, the adjustment tank (3) from the bath (1) the temperature difference between the yokon T1 of the inlet yokon (T3-ΔT _fall) and a bath (1) of the plating bath from entering the (T3-ΔT _fall - T1: hereinafter referred to as inflow bath temperature deviation) is greater than ± 10 ° C (T3-ΔT _fall -T1> 10 ° C, or T3-ΔT _fall -T1 <10 ° C), the dross produced in the plating bath 1 It has been found that the diameter sometimes exceeds the nominal diameter (for example, 50 µm). On the other hand, when the inflow bath temperature deviation is -10 ° C or more and 10 ° C or less (-10 ° C≤T3-ΔT _fall -T1≤10 ° C), a dross having a diameter sufficiently smaller than the noxious diameter (for example, about 22 μm or less) Only generated Therefore, in order to suppress generation | occurrence | production of a noxious diameter dross in the plating tank 1, it can be said that it is preferable that inflow bath temperature variation is -10 degreeC or more and 10 degrees C or less. In other words, the bath temperature T3 of the adjustment tank 3 is ± 10 with respect to the temperature ΔT _fall + T1 which added the bath temperature drop width ΔT _fall at the time of sending water from the adjustment tank 3 to the plating tank 1 to the bath temperature T1 of the plating tank 1. It can be said that what is in the range of ° C (T1 + ΔT _fall −10 ≦ T3 ≦ T1 + ΔT _fall +10) is preferable. Conventionally, in the plating bath, when the bath temperature variation of a plating bath generate | occur | produces, it was anticipated that dross | generation generation and growth are accelerated | stimulated. However, the range of specific bath temperature variation which encourages generation of noxious diameter dross was not clear. From the results of this experiment, in order to suppress the generation of harmful diameter dross in the plating bath 1, the bath temperature T3 of the adjustment tank is within a range of ± 10 ° C relative to the temperature of the bath temperature drop width ΔT _{fa ll} added to the bath temperature T1 of the plating bath. It turned out to be.

While the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to these examples. As long as the person having ordinary knowledge in the technical field to which the present invention belongs, it is obvious that various modifications or modifications can be made within the scope of the technical idea described in the claims. It is understood that it belongs to the technical scope of this invention.

The present invention is not limited to an alloyed hot dip galvanized steel sheet (GA), and the specific gravity of the hot dip galvanized steel sheet (GI), the hot dip zinc-aluminum alloy plated steel sheet produced only by the top dross, and the specific gravity is the top dross (Fe ₂ Al). _It is widely applicable to the molten zinc-aluminum alloy plated steel sheet manufactured using the plating bath 10 larger than the specific gravity of ₅ ). When the content of aluminum increases and the specific gravity of the plating bath 10 is less than the specific gravity of the top dross, the dross, which is a requirement of the present invention, cannot be separated. Therefore, the application range of this invention is a molten zinc-aluminum alloy plated steel plate whose aluminum content is less than 50 mass%.

In addition, in the varieties using a plating bath having a high aluminum content except for the alloyed hot dip galvanized steel sheet, it is not necessary to change the bath composition of the separation tank 2 and the adjustment tank 3 as in the above-described embodiment, and simply the bath temperature T By controlling this, it is possible to obtain a plating bath 10 containing almost no top dross. Thereby, it is possible to solve problems such as deterioration of the surface appearance due to dross adhesion, pressure scratches caused by dross, roll slip due to dross deposition on the roll surface in the bath, and the like.

According to the present invention, it is possible to efficiently and effectively remove dross generated inevitably in the plating bath at the time of production of an alloyed hot dip galvanized steel sheet, and to be almost completely harmless, which is industrially useful.

1: plating bath
2: Separation tank
3: adjustment tank
4: pre-melt tank
5: molten metal transfer device
6, 7: communication tube
8: transfer pipe
9: overflow pipe
10, 10A, 10B, 10C: plating bath
11: steel sheet
12: sink roll
13: gas wiping nozzle

Claims (11)

A plating bath for plating a steel plate immersed in the plating bath, having a first heat insulating part for insulating a plating bath which is a molten metal containing molten zinc and molten aluminum at a predetermined bath temperature T1;
A first heat insulating part for insulating the plating bath transferred from the plating bath outlet of the plating bath to a bath temperature T2 lower than the bath temperature T1 and containing aluminum having a higher concentration than the aluminum concentration A1 in the plating bath in the plating bath; Separation tank which floats and separates the precipitated top dross by making aluminum density | concentration A2 in the said plating bath conveyed from the said plating tank into 0.14 mass% or more by zinc-containing current spreading,
The second zinc-containing containing which has the 3rd heat insulating part which heat-retains the said plating bath conveyed from the said separation tank to bath temperature T3 higher than the said bath temperature T2, and contains aluminum of lower concentration than the said aluminum concentration A2, or does not contain aluminum. An adjustment tank for adjusting aluminum concentration A3 in the plating bath transferred from the separation tank to a concentration higher than the aluminum concentration A1 and lower than the aluminum concentration A2 by replenishment of
An apparatus for producing an alloyed hot-dip galvanized steel sheet, comprising a circulation section for circulating the plating bath in the order of the plating bath, the separation bath, and the adjustment bath. The aluminum concentration measuring unit for measuring the aluminum concentration A1 in the plating bath in the plating bath, further comprising:
The said circulation part controls the circulation amount of the said plating bath according to the measurement result of the said aluminum concentration measuring part, The alloying hot dip galvanized steel plate manufacturing apparatus characterized by the above-mentioned. The molten zinc alloy according to claim 1, wherein the bath temperature T2 of the separation tank is controlled by the second heat insulating part so as to be 5 ° C or more lower than the bath temperature T1 of the plating bath and to be equal to or higher than the melting point of the molten metal. Galvanized steel sheet manufacturing device. The bath temperature drop width of the plating bath at the time of transferring from the adjustment tank to the plating bath is set to ΔT _fall in degrees Celsius, wherein the bath temperature T1, the bath temperature T2, and the bath temperature T3 are set to degrees Celsius. The bath temperature T3 is controlled by the third heat retaining unit so as to satisfy the following equations (1) and (2).
[Equation 1]

&Quot; (2) &quot;

The method of claim 1, further comprising a pre-melt bath for melting the second zinc-containing now,
An apparatus for producing an alloyed hot-dip galvanized steel sheet, characterized in that the molten metal of the second zinc-containing molten metal melted in the premelt bath is supplied to the plating bath in the adjustment tank. The apparatus for producing an alloyed hot dip galvanized steel sheet according to claim 1, wherein the circulation section includes a molten metal transfer device provided in at least one of the plating tank, the separation tank, and the adjustment tank. The plating bath outlet of the plating bath is located downstream of the traveling direction of the steel plate so that the plating bath flows out from an upper portion of the plating bath by the flow of the plating bath accompanying the running of the steel plate. An alloyed hot-dip galvanized steel sheet manufacturing apparatus, characterized in that there is. The said plating bath, the said separation tank, or the said adjustment tank is comprised by dividing one tank by the weaving part,
An apparatus for producing an alloyed hot-dip galvanized steel sheet, characterized in that the bath temperature of each tank partitioned by the weir is independently controlled. The alloying hot-dip galvanized steel sheet manufacturing apparatus according to claim 1, wherein the amount of storage of the plating bath in the plating bath is 5 times or less of the circulation amount of the plating bath per hour by the circulation portion. The alloying hot-dip galvanized steel sheet manufacturing apparatus according to claim 1, wherein the storage amount of the plating bath in the separation tank is two times or more the circulation amount of the plating bath per hour by the circulation unit. While circulating the plating bath which is a molten metal containing molten zinc and molten aluminum in order of a plating tank, a separation tank, and an adjustment tank,
In the plating bath, the plating bath transferred from the adjusting tank is stored at a predetermined bath temperature T1 to plate the steel plate immersed in the plating bath,
In the separation tank, the plating bath transferred from the plating bath to the separation bath is stored at a bath temperature T2 lower than the bath temperature T1 of the plating bath, and contains a higher concentration of aluminum than the aluminum concentration A1 in the plating bath in the plating bath. By spreading the first zinc-containing now, aluminum concentration A2 in the plating bath transferred from the plating bath is 0.14 mass% or more, and the precipitated top dross is separated and floated,
In the adjustment tank, the plating bath transferred from the separation tank is stored at a bath temperature T3 higher than the bath temperature T2 of the separation tank to contain aluminum having a lower concentration than aluminum concentration A2 in the plating bath of the separation tank, or no aluminum. Alloying characterized in that the aluminum concentration A3 in the plating bath conveyed from the separation tank is adjusted to a concentration higher than the aluminum concentration A1 and lower than the aluminum concentration A2 by the diffusion of the second zinc-containing zinc. Method for manufacturing hot dip galvanized steel sheet.

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